Upper Miocene Echinoids from the ... - Smithsonian Institution

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Upper Miocene Echinoids from the Yorktown Formation of Virginia and Their Environmental Significance

SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY [9 7<2 NUMBER 13

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SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

13 Porter M. Kier Upper Miocene Echinoids from the Yorktown

Formation of Virginia

and Their Environmental Significance

I S S U E D

JW>R 1 0 1 9 7 2

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1972

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Porter M . Kier. U p p e r Miocene Echinoids from t h e Yorktown F o r m a t i o n of Virginia a n d T h e i r E n v i r o n m e n t a l Significance. Smithsonian Contributions to Paleobiology, n u m b e r 13, 41 pages, 7 figures, 10 plates. 1972.—Five echinoid species are described from the u p p e r Miocene p a r t of the Yorktown F o r m a t i o n of V i r g i n i a : Echinocardium orthonotum ( C o n r a d ) , Arbacia imporcera ( C o n r a d ) , Psammechinus philanthropus ( C o n r a d ) , Mellita aclinensis Kier, a n d Spatangus glenni Cooke. T h e assemblage probably lived in shallow, w a r m - t e m p e r a t e waters, E. orthonotum deeply buried n e a r shore, S. glenni shallowly buried offshore, a n d M. aclinensis with its test just covered near shore. Arbacia improcera a n d P. philan- thropus presumably lived together intertidally a n d n e a r shore, P. philanthropus living in holes in the i n d u r a t e d sediments or on the sand with its test covered with debris, whereas A. improcera probably was easily visible with nothing covering its test. Specimens formerly referred to E. orthonotum from the middle Miocene C h o p - tank F o r m a t i o n from M a r y l a n d are referred to E. marylandiense, n e w species.

Echinocardium gothicum ( R a v e n e l ) , from the Bear Bluff F o r m a t i o n of South Carolina, is considered a junior subjective synonym of E. orthonotum.

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Porter M. Kier Upper Miocene Echinoids from the Yorktown

Formation of Virginia

and Their Environmental Significance

Introduction

Although three species of echinoids have been described from the Yorktown Formation (upper Miocene lower Pliocene), these species were based on few specimens. Now that a large collection of echinoids from this formation has been studied, these species are redescribed herein and two additional species reported. This collection was made by Mr.

Warren Blow, presently with the Paleontology and Stratigraphy Branch of the United States Geological Survey, who started collecting fossils from the York- town Formation eight years ago. Since that time, he has accumulated hundreds of echinoids, which he has presented to the National Museum of Natural His- tory, Smithsonian Institution (under the catalog numbers of the United States National Museum: U S N M ) . Many of these specimens were collected in fragments that Blow painstakingly reassembled. He collected four large slabs containing hundreds of echinoids preserved within the sediment. Some of the specimens are extraordinarily well preserved with their apical systems, spines, pedicellariae, anal plates, and lanterns still intact, and many have their original color. Speci- mens of one of the species have food particles or fecal Porter M. Kier, Department of Paleobiology, National Mu- seum of Natural History, Smithsonian Institution, Washing- ton, D.C. 20560.

pellets still preserved in their tests. The study of this large collection permits a more definitive description of the species, resulting in a better understanding of their relationship to other species, and some interpre- tation of the environment in which they lived.

The echinoid assemblage consists of: Echinocard- ium orthonotum (Conrad), Arbacia improcera (Con- rad), Psammechinus philanthropus (Conrad), Mel- lita aclinensis Kier, and Spatangus glenni Cooke. The first three species had been described previously from the Yorktown, but Echinocardium orthonotum was thought to include also specimens from the middle Miocene Choptank Formation from Maryland. These Maryland specimens are distinct and are referred to a new species described herein, Echinocardium mary- landiense. Four specimens of Mellita aclinensis are present, a species known heretofore only from the upper Miocene Tamiami Formation in Florida, and one specimen of Spatangus glenni, previously known only from upper Miocene or Pliocene deposits in South Carolina.

Acknowledgments

I thank Warren C. Blow for collecting and preparing most of the echinoids described in this paper and for his great generosity in presenting the specimens to the National Museum of Natural History. These echin-

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oids are some of the best-preserved fossil echinoids known, a n d their availability to science is d u e to his patient a n d preservering efforts. I a m m u c h indebted to J . E. Hazel of the U n i t e d States Geological Survey, ( U S G S ) , who not only critically read the m a n u s c r i p t b u t also provided m u c h of the information on the paleoclimatology of the Miocene of the region of the deposition of the Yorktown F o r m a t i o n a n d provided a comparison with the present climate of this area.

D r u i d Wilson, also of the U n i t e d States Geological Survey, collected m a n y of the South Carolina speci- m e n s discussed in this p a p e r a n d provided m u c h information on the stratigraphy of the beds from where they were collected. Blake W. Blackwelder, w h o is n o w studying the mollusks of the Bear Bluff F o r m a - tion, gave m e his preliminary opinions on the age of this formation, a n d R i c h a r d E. G r a n t of the U n i t e d States Geological Survey a n d D a v i d L. Pawson of the N a t i o n a l M u s e u m of N a t u r a l History, Smithsonian Institution, reviewed the p a p e r a n d m a d e m a n y pertinent suggestions. L a u c k W . W a r d provided valuable information on the relative age of the Vir- ginia localities.

T h o m a s F . Phelan not only did the p h o t o g r a p h y b u t also m a d e the remarkable reconstruction of a dis- associated lantern of Psammechinus philanthropus figured on Plate 2 : figures 7, 8. L a r r y I s h a m , the scientific illustrator for the D e p a r t m e n t of Paleobi- ology in the N a t i o n a l M u s e u m of N a t u r a l History m a d e the locality m a p a n d the superb reconstruction of the living habits of the Miocene echinoids on Figure 2.

H o r a c e R i c h a r d s of the A c a d e m y of N a t u r a l Sci- ences of Philadelphia lent specimens a n d searched for one of C o n r a d ' s lost types, a n d N o r m a n F . Newell provided locality d a t a on one of the type-specimens in the A m e r i c a n M u s e u m of N a t u r a l History ( A M N H ) .

Stratigraphy

T h e Y o r k t o w n F o r m a t i o n consists of fossiliferous, silty sands a n d sandy silts t h a t crop out in southeastern Virginia a n d northeastern N o r t h Carolina, from the R a p p a h a n n o c k River in Virginia to the Neuse River in N o r t h Carolina. Most of the echinoids (represent- ing all the species) c a m e from four localities, two of which have been d a t e d by Hazel ( 1 9 7 1 a ) . H e has just completed a biostratigraphic study of the ostracodes of t h e Yorktown, identifying 230 species a n d dividing

the formation into three ostracode assemblage zones.

T h e oldest zone, the Ptery go cythereis inexpectata Zone, a n d the m i d d l e Orionina vaughani Zone are considered' by Hazel to be late M i o c e n e , a n d his u p - permost zone, the Puriana mesacostalis Z o n e , is considered by him to be early Pliocene. T h e two echinoid localities, a n d probably the third a n d fourth at a n d n e a r M o g a r t ' s Beach, belong to Hazel's Orionina vaughani Zone. T h i s zone a p p r o x i m a t e s Mansfield's

(in G a r d n e r , 1943) Turritella alticostata Z o n e , which Mansfield also considered to be late Miocene. Gibson (1967) likewise considers these beds as late Miocene.

W a r r e n C. Blow a n d L a u c k W . W a r d (personal c o m m u n i c a t i o n , 1971) h a v e m a d e extensive collections from these four localities a n d believe t h a t , on the basis of the molluscan assemblages, they are roughly equivalent in age.

Paleoenvironment

C L I M A T E . — H a z e l (1971b) has also m a d e a paleo- climatological study of the Y o r k t o w n F o r m a t i o n based on the ostracodes, a n d h e concludes t h a t the climate was m o r e equable a n d w a r m e r in the winter d u r i n g the deposition of the Y o r k t o w n t h a n it n o w is in the same region. Fifty-nine of the ostracode species found in the Y o r k t o w n are still living, a n d , as a result, Hazel is able to m a k e well-substantiated estimates of the Y o r k t o w n climate. T h e Orionina vaughani Zone (where the echinoids occur) con- tains 40 surviving ostracode species. These ostracodes indicate t h a t b o t t o m t e m p e r a t u r e s averaged n o cooler t h a n 12.5°C in the coldest m o n t h a n d t h a t the sum- m e r m a x i m u m averaged below 2 0 ° C in the older p a r t of the zone a n d less t h a n 25 ° C in the m i d d l e a n d younger parts. Hazel believes t h a t , d u r i n g deposition of the Orionina vaughani Zone, the yearly range in b o t t o m t e m p e r a t u r e was only a b o u t 5 ° C to 1 0 ° C . T h i s equable t h e r m a l regime is m a r k e d l y different from t h a t of any province a n d c o n c o m i t a n t climate zone n o w e x t a n t along the Atlantic coast of the U n i t e d States. T h e t e m p e r a t u r e s varied from about 1 2 ° C to 1 5 ° C in the winter to a b o u t 1 7 . 5 ° C to 2 0 ° C a n d finally to 2 0 ° C to 2 5 ° C in s u m m e r . T h i s p a r t i c u l a r t h e r m a l regime, Hazel believes, is indica- tive of w a r m - t e m p e r a t e conditions analogous to t h a t represented by the L u s i t a n i a n Province of western E u r o p e . A w a r m - t e m p e r a t e zone is not present along the Atlantic coast of N o r t h America today ( D a n a ,

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1853; Hall, 1964; Hazel, 1970). The offshore climate of the study region today is mild-temperate with the bottom temperature in inner sublittoral waters aver- aging about 5°C to 7.5°C in the coldest month and about 20°C to 25°C in the warmest month.

The Yorktown echinoids, like the ostracodes, indicate a past climate warmer than now. Psammechinus philanthropus (Conrad) is very similar to the living P. miliaris (Miiller), so much so that small specimens of both species are almost indistinguishable. This living species occurs in cold-temperate to subtropical waters off European coasts from Trondheimfjord to the northwestern coast of Africa. Spatangus glenni Cooke is very similar to S. purpureus Miiller, also occurring in the same waters and in the Mediterranean.

Mellita aclinensis Kier has been found in the Tami- ami Formation of Florida, probably deposited in subtropical waters; it is very similar to M. quinquies- perforata (Leske), now living in mild-temperate to tropical waters along the eastern coast of America from Nantucket to the Brazilian coast as far south as Santos. Mellita quinquiesperforata, primarily a tropical-subtropical species, is scarce north of Cape Hat- teras. Arbacia improcera (Conrad) resembles A.

punctulata (Lamarck), which lives in mild-temperate to tropical waters from Cape Cod through the Carib- bean and in Yucatan. Echinocardium orthonotum

(Conrad) is not useful in evaluating past climate because it resembles the living species E. cordatum

(Pennant), which is virtually cosmopolitan in cold- temperate to tropical waters.

Although some of these living species range into cooler waters, they all occur in subtropical regions, suggesting that the fossil echinoids they resemble lived in waters warmer than the mild-temperate waters now occurring off the coast of Viriginia.

LIVING HABITS OF T H E ECHINOIDS.—Most of the

fossil species are very similar to species now living, and it is therefore possible to make well-substantiated assumptions on the living habits of these fossil echinoids (see Figure 1).

Arbacia improcera resembles A. punctulata (La- marck) living off the coast of Virginia. Presumably its living habits were similar to A. punctulata, which is found in its greatest numbers in shallow water 5 to 20 feet deep on rock or sand bottoms. This species according to Sharp and Gray (1962) and Kier and Grant (1965:17-18) is highly variable in its response to light, with some specimens remaining exposed to

the full light of the sun and others seeking cover. Like A. punctulata, A. improcera probably lacked sucking disks on its adapical tubefeet and, therefore, was un- able to cover itself with debris. It presumably did not excavate holes in the rocky shores (no living Arbacia can). It has many porepairs on the adoral surface, and the large number of tubefeet extending from them would have made it possible for the animal to cling tenaciously to intertidal rocks that were exposed to wave action. These tubefeet had sucking disks, as indicated by the presence of a ridge between the pores of each porepair, for the attachment of muscles used to retract these prehensile tubefeet (Nichols,

1959a: 421; Chesher, 1968:17).

Psammechinus philanthropus (Conrad) is strikingly similar to P. miliaris, and presumably it lived sim- ilarly in the littoral zone on rock or sand. It probably lived with Arbacia improcera, but it doubtless had sucking disks on its adapical tubefeet (they occur in P. miliaris), and, therefore, it may have had its test covered with algae and other foreign debris. Some individuals might have lived in holes burrowed into rock.

Mellita aclinensis Kier is very like M. quinquiesper- / or at a (Leske) and presumably lived like it in shallow water on a firm sand bottom. It would have been slightly buried, with not more than 20 to 30 mm of sediment on top of its test.

Spatangus glenni is very similar to S. purpureus Miiller now living off the British Isles. Owing to the research of Nichols (1959a, 1959b, 1962), the living habits of this British species are well known. Spa- tangus glenni shares enough morphological features with S. purpureus to suggest that the fossil species lived like the Recent ones in shallow water, that is, offshore, burrowing approximately 2 cm into coarse sediment. Spatangus glenni has a bilobed subanal fasciole that is also present in S. purpureus, where it is used to maintain, in the sediment, two horizontal tubes lying parallel to each other and originating at each lobe of the fasciole. These tubes provide a drain- away for the waste products of respiration and defe- cation, which are transported to the posterior region of the echinoid by cilia. This current is greatly en- hanced and directed away from the test down the twin tubes by the densely ciliated small spines in the subanal fasciole. According to Nichols (1962:116), two tubes are necessary in S. purpureus because the echinoid lives in coarse sediment that is subject to

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caving. T h e e x t r a tube provides oxygen for the echinoid while it reopens a blocked tube. L o n g prehensile tubefeet found within the fasciole are used to excavate these tubes a n d to plaster their sides with m u c u s . T h e presence of large pores within the fasciole of S. glenni indicates t h a t it also h a d these tubefeet.

Commonly, spatangoids t h a t b u r r o w deeply in the substrate h a v e a tube extending from the dorsal surface of the test to the top of the substrate. T h i s tube provides a c h a n n e l for w a t e r currents t h a t are directed over t h e respiratory tubefeet of the petals.

Spatangus purpureus ( a n d S. glenni as indicated by the presence of large tubercles) has large spines on the adapical surface t h a t help keep a n opening to the surface w h e n the echinoid is b u r r o w e d only slightly, but both species lack the structures necessary to m a i n - tain a long tube. T h e porepairs in the anterior a m - b u l a c r u m of S. glenni are very small a n d lack any protuberances between the pores of a pair for the at- t a c h m e n t of the muscles t h a t are used to retract the long tubefeet necessary to excavate a n d m a i n t a i n a t u b e ; however, S. purpureus, in spite of the lack of a dorsal tube, it able to burrow because it lives in coarse substratum t h a t has large interstices t h r o u g h which the currents can pass.

Because the subanal fasciole in S. glenni is less strongly bilobed t h a n in S. purpureus a n d there are fewer adapical tubercles, resulting in fewer large spines, S. glenni was probably able to b u r r o w slightly less deeply t h a n S. purpureus.

Although Echinocardium orthonotum is also a spatangoid, it probably lived somewhat differently t h a n Spatangus glenni. It is very similar a n d has all the functional morphological features of the living E.

cordatum ( P e n n a n t ) . Considerable research has been done on this living species; Nichols (1959a) in par- ticular has studied its living habits and c o m p a r e d t h e m to S. purpureus. Although S. purpureus ( a n d presumably S. glenni) burrows only to a level 2 cm beneath the surface of the substratum, E. cordatum burrows m u c h deeper, to a d e p t h of 10 to 20 cm. Ac- cording to Nichols, E. cordatum, because it commonly lives n e a r shore on sandy beaches, must b u r r o w deeply in order to avoid being left high a n d dry by the receding tide, whereas S. purpureus lives far enough offshore to be unaffected by tides. Echino- cardium cordatum builds a n d m a i n t a i n s a long b r e a t h i n g tube to the surface and has an inner fasci-

ole on its dorsal surface in order to d r a w w a t e r d o w n the funnel a n d across the respiratory petals. Likewise, E. orthonotum has a n inner fasciole a n d presumably also has constructed a funnel. Because Echinocardium cordatum a n d E. orthonotum do n o t h a v e bilobed subanal fascioles as do S. purpureus a n d S. glenni, they could construct only one sanitary tube for the removal of waste products instead of two as in the two species of Spatangus. Finally, a l t h o u g h E. cordatum lives on beaches n e a r shore, it is not found in areas subject to heavy wave or c u r r e n t action.

I n s u m m a r y (Figure 1 ) , Arbacia improcera a n d Psammechinus philanthropus would be living in the intertidal a n d littoral zones on rock or sand, P. phil- anthropus in holes in the rock or covered with debris, b u t A. improcera would be easily visible with its test uncovered. Living also n e a r shore, deeply buried in the sand, would be Echinocardium orthonotum with a long funnel e x t e n d i n g above its test to the surface of the substratum a n d a single tube e x t e n d i n g posteriorly. T h e sand dollar, Mellita aclinensis, would be found n e a r shore at a d e p t h of 3 to 15 meters with its test slightly buried. Finally, farther offshore Spa- tangus glenni would be b u r r o w e d only a few centi- meters in the sand, with no funnel to the surface, b u t with its adapical spines holding open a passage to the respiratory tubefeet, a n d with two tubes extending posteriorly.

C O N D I T I O N O F D E P O S I T I O N . — T h e s e echinoids are remarkably well preserved. Most of the regulars still have the parts of their lanterns intact inside their tests, a n d m a n y pedicellariae are present with the specimens. M a n y specimens of Psammechinus phil- anthropus still have food or fecal pellets preserved in their tests (Plate 2 : figure 2 ) .

Because lanterns a n d pedicellariae are lost after the death of the a n i m a l , it must be assumed t h a t the echinoids were covered with sediment at, or soon after, d e a t h ; otherwise, currents or the action of pred- ators would have broken u p the tests a n d disas- sociated the lanterns a n d pedicellariae. Echinoids, however, do not occur in the sediment in their living positions. Large slabs have been collected t h a t con- tain m a n y specimens of P. philanthropus a n d E. or- thonotum (Plate 9 : figure 3 ) , a n d these specimens are j u m b l e d with the tests in h a p h a z a r d position. I t is, therefore, probable t h a t these echinoids, while alive, were c a u g h t u p by storm currents a n d waves a n d covered by sediment. Possibly this deposition took

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NUMBER 13

Psammechinus

Mellita

FIGURE 1.—The probable life positions of the five echinoid species from the Yorktown Forma- tion: These fossil species are so like species now living that it is possible to make well- substantiated predictions of their living habits. The figures of Spatangus and Echinocardium are based on the figures and descriptions of Nichols (1959a) for Spatangus purpureus Miiller and Echinocardium cordatum (Pennant).

place near shore in shallow water perhaps 5 to 20 meters deep because the most common specimens are P. philanthropus and E. orthonotum, both species that are assumed to have lived near shore.

POST-DEPOSITION CONDITIONS.—Many of these echinoids still have their color, and many of the tests do not have the interstices of their plates filled with secondary calcite. This unusual preservation indicates that little leaching and recrystallization has occurred in the sediments since their deposition. The presence of organic material still preserved in the food or fecal pellets indicates restricted bacterial activity.

Relation to Other Fossil Echinoid Faunas

The Yorktown echinoid assemblage has affinities with echinoid assemblages from the upper Miocene or Plio- cene of South Carolina and Florida. Echinocardium orthonotum of the Yorktown is considered herein a senior synonym of E. gothicum (Ravenel), described by Ravenel (1848) and Tuomey and Holmes (1855) from Grove Plantation on the Cooper River in South Carolina. This species also occurs in spoil deposits in the Intracoastal Waterway canal, which Druid Wilson (personal communication, 1970) considers, on the

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basis of the mollusks, to be late Miocene and equivalent in age to the beds at Grove Plantation. Spatangus glenni, which is found in the Yorktown, is found also in these canal deposits. B. W. Blackwelder (personal communication, 1971), who is currently studying the mollusks, believes that these deposits are from the Bear Bluff Formation of Dubar (1969), which Dubar considers probably to be Pliocene.

The Yorktown species Arbacia improcera is very similar and may be conspecific with A. sloani (Clark) from upper Miocene beds in the Duplin Marl at Bos- tick Landing, Pee Dee River, South Carolina.

The Yorktown echinoid assemblage is also somewhat similar to the echinoids of the upper Miocene Tamiami Formation of Florida. Mellita aclinensis is found in both assemblages, and the Yorktown A. im- procera is probably synonymous with the Tamiami A.

crenulata Kier.

Localities

Most of the echinoids collected by Warren C. Blow came from the four localities in Virginia indicated in Figure 2 and described by him below. Hazel (1971a)

76°30' 76°I5

76°30' 76°I5'

F I G U R E 2. - T h e localities ( 1 - 4 ) where W a r r e n C. Blow collected most of his echinoids from the Yorktown F o r m a t i o n .

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has studied the ostracodes from localities 3 and 4 and considers them to be from his Orionina vaughani Zone of the Yorktown Formation. Both Warren Blow and Lauck W. Ward, who also has collected extensively in the Yorktown, consider all four localities to be in this zone.

LOCALITY 1 (USGS locality 25113) .—Future Homemakers of America-Future Farmers of Amer- ica [FHA-FFA] girls camp, approximately 3.6 miles NNE of Smithfield, south bank of James River,

Isle of Wight County (see Virginia quadrangle 7.5' Mulberry Island, 1965). A block of cemented coquina containing numerous specimens of Echinocardium orthonotum (Conrad) was found adjacent to 23-foot- high face of outcropping Yorktown Formation at a point between 100 and 300 yards ESE of the present camp staircase. This material undoubtedly was de- rived from a distinctive 1- to 2-foot-thick ledge of cemented coquina occurring approximately 21 feet above the beach, which terminates the Yorktown Formation along Mogarts Beach. Collectors: Edward E. Bottoms and Warren C. Blow. Species: Echino- cardium orthonotum (Conrad), Psammechinus phil- anthropus (Conrad).

LOCALITY 2.—Hunt club, south bank of James River, approximately 0.65 miles ESE of FHA-FFA girls camp at Mogarts Beach, Isle of Wight County (see Virginia quadrangle 7.5', Mulberry Island, 1965).

This locality begins at the mouth of a deep ravine (distinguishable by its two small lakes), approximately 100 feet WNW of the club house, and con- tinues ESE along the base of the bluffs overlooking the James River for approximately 200 yards.

USGS 25114: Echinoids collected in situ in very macrofossiliferous, aqua, silty sand between the beach level and not more than 6 feet above the beach. Col- lectors: Warren C. Blow and others from 1963-1967.

Species: Arbacia improcera (Conrad), Psammechinus philanthropus (Conrad), and Spatangus glenni Cooke.

USGS 25115: In situ in sparsely macrofossiliferous, aqua, silty sand, approximately 6.5 to 8.5 feet above beach level. Collectors: R. H. Bailey, B. Dyer, R. V. Blow, and W. C Blow, 1965-1967. Species:

Echinocardium orthonotum (Conrad).

USGS 25116: 100 yards ESE of ravine between 0 and 0.5 feet above beach level. Collectors: Richard H. Bailey and W. C. Blow, 1967. Species: Spatangus glenni Cooke.

USGS 25117: 158 yards ESE of ravine, 3 feet above beach level. Collector: W. C. Blow, 1968.

Species: Spatangus glenni Cooke.

LOCALITY 3.—Rice's Pit just N of the intersection of the Fox Hill Road (Virginia Highway 167), and the Harris Creek Road, Hampton City (see Virginia quadrangle 7.5', Hampton, 1965).

USGS 24810: Western wall of pit approximately 350 feet NNW of the upper SW corner; approximately 36 feet below local topography. Collectors: B.

Dyer and W. C. Blow, 1969. Species: Echinocardium orthonotum (Conrad).

USGS 25122, 25123: In situ from very macrofossiliferous, buff, silty sand of the upper 6 to 7 feet of the Yorktown Formation (approximately 6 to 12 feet below local topography along central portion of the southern half of the western wall of pit). Col- lectors: W. C. Blow, Barbara Grocys. Species: Ar- bacia improcera (Conrad), Psammechinus philan- thropus (Conrad), Mellita aclinensis Kier, and Echinocardium orthonotum (Conrad).

LOCALITY 4.—Lone Star Cement pit, 0.5 mile N of Chuckatuck, Nansemond County (see Virginia quadrangle 7.5', Chuckatuck and Beens Church, 1965).

USGS 24493: Western wall of pit approximately 300 yards from NW corner 1 to 3 feet above lake level, 24 feet below top of section. Collectors: W. C.

Blow and R. V. Blow, 1967. Species: Psammechinus philanthropus, Echinocardium orthonotum (Conrad).

USGS 24626: Western wall of pit, eastern face of cut 33. Collector: W. C. Blow, 1968. Species:

Echinocardium orthonotum (Conrad).

USGS 25119: Float of maroon chunks of semi- hardened, silty sand collected between the south- central and northernmost extent of the western wall of the pit. Collector: W. C. Blow, 1964. Species:

Echinocardium orthonotum (Conrad).

USGS 25120: Approximately 3 to 5 feet above the lake level (22 to 24 feet below local topography) along the central portion of the western wall of the pit. Collectors: W. C. Blow and E. E. Bottoms, 1964. Species: Echinocardium orthonotum (Con- rad).

USGS 25121: Material collected in situ (generally from a fine blue-gray hash) along the south- central and northern half of the western wall of pit, approximately 0 to 3 feet above lake level or 24 to 27 feet below local topography. Collectors: W. C. Blow and others, 1963—present. Species: Arbacia improcera

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( C o n r a d ) , Psammechinus philanthropus ( C o n r a d ) , Mellita aclinensis Kier, a n d Echinocardium ortho- notum ( C o n r a d ) .

Arbacia improcera ( C o n r a d )

P L A T E I

Echinus improcerus C o n r a d , 1843a: 310.

Psammechinus improcerus.—Stefanini, 1 9 1 2 : 7 0 5 . Coelopleurus improcerus.—Clark a n d Twitchell, 1 9 1 5 : 1 8 0 ,

pi. 8 4 : figs. 4 a - c .

Arbacia improcera.—Cooke, 1 9 4 1 : 1 1 , pi. 1: figs. 7-9.-—

Cooke, 1 9 5 9 : 2 0 , pi. 4 : figs. 1-3.—Kier, 1 9 6 3 : pi. 1:

fig. 6.

F o r m a n y years only one specimen has (in a d d i t i o n to the missing h o l o t y p e ) , tional specimens are n o w extant. T h e five of these specimens are as follows:

D i a m e t e r H e i g h t

D i a m e t e r of peristome Greatest w i d t h of

a m b u l a c r u m H e i g h t of i n t e r a m b u -

lacral p l a t e a t a m b i t u s W i d t h of i n t e r a m b u -

lacral plate at a m b i t u s N u m b e r of i n t e r a m b u -

lacral plates in single row

N u m b e r of porepairs in single poriferous zone Greatest w i d t h of apical

system

6.7 3.5

1.3

1.3 18.5

6.9 9.5 3.6 1.4 3.8

32.

16

b e e n a v a i l a b l e b u t five a d d i - d i m e n s i o n s of

7 29.5 36.5 0 13.2 15.0 13.3 16.4 .1 6.2 7.4 .7 2.5 2.7 .7 6.0 6.7

8.9 12.0 14.0 13.0 15.0 - 37.0 52.0 51.0 57.0 .3 - 10.0 2.8 5.9

C O M P A R I S O N W I T H O T H E R S P E C I E S . — A r b a c i a im- procera m a y be conspecific with A. sloani ( C l a r k ) from u p p e r Miocene beds in the D u p l i n M a r l at Bos- tick L a n d i n g , Pee D e e River, South Carolina. O n l y one specimen of A. sloani, the holotype, is k n o w n , a n d it is similar in most of its dimensions to A. improcera, h a v i n g the d i a m e t e r of its peristome 50 percent of the d i a m e t e r of its test ( D ) , w i d t h of an a m b u l a c r u m at the a m b i t u s 20 percent D , height of a n i n t e r a m b u l a - cral plate at the a m b i t u s 2.0 percent D , w i d t h 5.5 percent D , greatest width of the apical system 7.3 percent D , n u m b e r of i n t e r a m b u l a c r a l plates in single row 14, a n d n u m b e r of porepairs in a single poriferous zone 5 5 . Cooke ( 1 9 5 9 : 2 1 ) considered t h a t the two species were very similar a n d m i g h t be synonymous, b u t h e also noted t h a t they differed, with A.

improcera h a v i n g a lower test a n d a m o r e rugose

o r n a m e n t a t i o n . T h e only specimen of A. improcera t h a t h e h a d available is lower t h a n t h e holotype of A. sloani, w h i c h h a s a height 41 p e r c e n t of its di- a m e t e r as opposed to 53 p e r c e n t in A. sloani. O n e of the recently acquired specimens of A. improcera, however, has a height e q u a l to 49 p e r c e n t D . T h i s difference from A. sloani is slight a n d , until m o r e specimens h a v e been found, its significance c a n n o t be evaluated. A l t h o u g h Cooke considered t h e o r n a m e n - tation in the n a k e d a d a p i c a l i n t e r a m b u l a c r a l areas different in the t w o species, I can see no distinguishing dissimilarities ( c o m p a r e Plate 1: figure 5 to Plate 2 : figure 1 ) . W h e n m o r e specimens are available, it should be possible to d e t e r m i n e w h e t h e r these two species are s e p a r a t e or synonymous, b u t , until t h e n , it seems best n o t to a t t e m p t to m a k e this decision.

Arbacia improcera differs from A. rivuli Cooke from the late M i o c e n e (?) in S o u t h C a r o l i n a in having its a d a p i c a l i n t e r a m b u l a c r a m o r e n a k e d . I n A.

improcera only a single row of tubercles occurs on each column of i n t e r a m b u l a c r a l plates d o w n to a point n e a r the a m b i t u s , whereas in A. rivuli a second row extends almost to the apical system. Arbacia im- procera differs from A. waccamaw Cooke also from t h e late Miocene (?) in S o u t h C a r o l i n a in h a v i n g wider a n d lower a d a p i c a l i n t e r a m b u l a c r a l plates.

Arbacia improcera m a y be conspecific with A. cren- ulata K i e r from t h e late M i o c e n e T a m i a m i F o r m a - tion of Florida. W h e n I described A. crenulata, only one specimen of A. improcera was available for comparison. O n this specimen the o r n a m e n t a t i o n was decidedly different from t h a t of A. crenulata. I n A.

crenulata the o r n a m e n t a t i o n consists of fine crenulations, whereas in the single specimen of A. improcera they were g r a n u l e s ; however, on the n e w specimens of A. improcera these granules c o m m o n l y are joined together into crenulations. T h e s e two species a r e p r o b - ably synonymous, b u t m o r e specimens are needed in order to k n o w the extent of the v a r i a t i o n of this o r n a - m e n t a t i o n within one p o p u l a t i o n .

Arbacia improcera is similar in t h e following dimensions to A. punctulata ( L a m a r c k ) , n o w living off the coast of V i r g i n i a : height, d i a m e t e r of peristome, w i d t h of a m b u l a c r u m , w i d t h of apical system, n u m - ber of i n t e r a m b u l a c r a l p l a t e , and n u m b e r of porepairs. It differs in h a v i n g only two large tubercles on each i n t e r a m b u l a c r a l plate a t the a m b i t u s , whereas t h e r e are t h r e e in specimens of t h e same size in A.

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NUMBER 13

punctulata. Moreover, in A. improcera the naked zones in the interambulacra extend farther adorally.

LOCALITIES.—Blow's localities 2 (USGS 25114), 3 (USGS 25122), 4 (USGS 25121), J. T. Williams' marl pit, Smith County, 0.5 mile below the dam at Suffolk waterworks, collected by M. W. Twitchell.

USGS 24817, exposed face of high bluff (approximately 500 feet NW of cemetery), south bank of Nansemond River, 0.5 mile downstream from Vir- ginia Highways 10 and 32 bridge, Suffolk City, Vir- ginia, from fossiliferous, bluff, silty sand, 3 feet above beach level, collected by Brian Dyer and Warren C.

Blow; Bank of Nansemond River rising from tidal flats at Suffolk, Virginia, collected by W. C. Mans- field. The holotype came from the James River near Smithfield.

TYPE-SPECIMENS.—Location of holotype not known; figured specimens: USNM 166487, 17449.

Psammechinus philanthropus (Conrad)

F I G U R E 3 ; P L A T E 2 : F I G U R E S 2 - 8 ; P L A T E 3 ; P L A T E 4 : F I G U R E S 1, 3 ; P L A T E 5 : F I G U R E S 1, 3

Echinus philanthropus C o n r a d , 1843a: 3 1 0 . — C o n r a d , 1846:

220.

Psammechinus philanthropus.—Meek, 1864:2.—Stefanini, 1 9 1 2 : 7 0 5 . — C l a r k e a n d Twitchell, 1 9 1 5 : 1 8 1 , pi. 8 4 : figs.

Ga-c.~Cooke, 1 9 4 1 : 1 6 . — C o o k e , 1959: 16, pi. 3 : figs. 1, 2.

Echinus ruffini Forbes in Lyell, 1 8 4 5 a : 4 2 6 , figs, la—d [and Lyell, 1 8 4 5 b : 5 6 0 , 2 figs.].—Desor, 1 8 5 8 : 1 2 1 . — E m m o n s , 1 8 5 8 : 3 0 6 , figs. 239a-d.—Stefanini, 1 9 1 2 : 7 0 5 .

MATERIAL.—Hundreds of extremely well-preserved specimens have been collected by Robert V. Blow and Warren C. Blow. Many of them are on two large slabs. These specimens are arranged haphazardly, in- dicating that they are not in life position, but the presence of lanterns, apical systems, and spines on many of the specimens indicates that they were buried soon after death. Because in the past only a few specimens have been available, this species has never been ade- quately described. The description and statistics below are based on 30 specimens from the same locality

(Blow locality 4, USGS 24493).

SHAPE AND SIZE.—Diameter (D) varying from 14.0 to 39.3 mm, mean 21.1 (SD 5.4, CV 25.6, N - 3 0 ) , height varying from 46 to 61 percent D (SD 3.5, CV 6.6, N - 3 0 ) , height not varying with size of specimen;

marginal outline of test circular to slightly subpentag-

onal with apices at ambulacra; test slightly depressed at peristome.

APICAL SYSTEM.—All oculars exsert (Figure 3 ) , genital 2 larger than other genital plates, one or two tubercles on each genital, periproct oblique with long axis passing through genital 2 and ocular V.

AMBULACRA.—Narrow, width 23-26 percent D, mean 24.8 (SD 0.7, CV 3.1, N - 3 0 ) ; plates trigemi- nate, 15 compound plates in single poriferous zone of smallest specimen 14.0 mm in diameter, 20 in specimen 21 mm in diameter, 26 in largest 39.3 mm in diameter, with a mean 18.8 plates (SD 2.5, CV 13.3, N - 3 0 ) .

INTERAMBULACRA.—Plates low, at ambitus 1.2 compound ambulacral plates for each interambulacral plate; 13 plates in single column of smallest specimen 14.0 mm in diameter, 16 in specimen 21.0 mm, 22 in largest 39.3 mm in diameter, mean 15.6 (SD 2.1, CV 13.2, N - 3 0 ) .

PERISTOME.—Pentagonal with apices in interambulacra, large, diameter varying from 36 to 52 percent D, mean 44.8 (SD 3.1, CV 6.8, N - 3 0 ) .

TUBERCULATION.—Ambulacra; two vertical rows of primary, imperforate, noncrenulate tubercles in each

FIGURE 3.—Psammechinus philanthropus ( C o n r a d ) : Apical system of U S N M 174452 from Blow's locality 4 ( X 1 0 ) . (A p h o t o g r a p h of this region is on Plate 3 : figure 4.)

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a r e a ( P l a t e 3 : figure 2) with t w o inner rows almost equally developed a t a m b i t u s in larger specimens

( P l a t e 5 : figure 1) ; in small specimens only two rows a t a m b i t u s , i n n e r tubercles slightly developed (Plate 4 : figure 1 ) ; p r i m a r y tubercles occupy most of height of p l a t e .

I N T E R A M B U L A C R A . — I n large specimens a t a m b i t u s 5 - 8 imperforate, n o n c r e n u l a t e tubercles a r r a n g e d in 1—2 i r r e g u l a r horizontal rows ( P l a t e 5 : figure 3 ) , in small specimens t w o vertical rows of tubercles at a m - bitus with a single large tubercle in m i d d l e of each plate with a smaller tubercle on either side ( P l a t e 4 : figure 3) ; as echinoid increases in size, these smaller tubercles increase in size relative to t h e central tubercle until they a r e of e q u a l size a n d t h e t w o vertical rows a r e n o longer distinguishable.

PEDICELLARIAE.-—Tridentate a n d ophicephalous pedicallariae found ( P l a t e 2 : figures 3 - 6 ) .

LANTERN.-—Preserved on most specimens (Plate 2 : figures 7, 8 ) .

C O L O R . — P r e s e r v e d on all specimens, d a r k b r o w n b a n d r u n n i n g d o w n center of a m b u l a c r a ; lighter or a d a r k b r o w n b a n d r u n n i n g d o w n center of i n t e r a m - b u l a c r a .

C O M P A R I S O N W I T H O T H E R S P E C I E S . — T h i s species is very similar a n d obviously closely related to Psam- mechinus miliaris ( M i i l l e r ) , n o w living along t h e E u r o p e a n coasts from t h e T r o n d h e i m f j o r d a n d Ice- l a n d to t h e n o r t h w e s t e r n coast of Africa. I m e a s u r e d t h e d i a m e t e r , height, d i a m e t e r of peristome, w i d t h of a m b u l a c r u m , a n d n u m b e r of i n t e r a m b u l a c r a l a n d a m - b u l a c r a l plates of a collection of both species a n d tested t h e m statistically to see w h e t h e r or n o t they differed significantly. N o significant difference is pres- e n t in the height of t h e test, w i d t h of a m b u l a c r a , a n d n u m b e r of a m b u l a c r a l plates, b u t t h e two species differ in t h e d i a m e t e r of their peristomes a n d t h e n u m - b e r of i n t e r a m b u l a c r a l plates. Psammechinus philan- thropus has a larger peristome a n d m o r e i n t e r a m b u - lacral plates t h a n P miliaris, with a peristome whose d i a m e t e r is 44.8 p e r c e n t t h e d i a m e t e r of t h e test as opposed to 39.7 p e r c e n t in P. miliaris, a n d a n average of 15.6 i n t e r a m b u l a c r a l plates in each half-column as opposed to 16.1 in t h e living species. A student t test was r u n on t h e difference of these m e a n s , a n d they are significant to . 0 0 1 .

T h e t u b e r c u l a t i o n of P. philanthropus (Plate 5 : figures 1, 3) differs in large specimens in h a v i n g at least five tubercles on each i n t e r a m b u l a c r a l plate at

the ambitus of a p p r o x i m a t e l y e q u a l size, whereas in P. miliaris one tubercle is larger t h a n all t h e others ( P l a t e 5 : figures 2, 4 ) . T h i s difference, however, is not present in small specimens. Specimens of t h e t w o species 14 ' m m in d i a m e t e r a r e indistinguishable in their t u b e r c u l a t i o n . T h e small P. philanthropus

(Plate 4 : figures 1, 3) h a s o n e larger tubercle on each plate just as in P. miliaris ( P l a t e 4 : figures 2, 4 ) ; however, t h e difference in size of t h e peristome is persistent in all t h e specimens regardless of their size.

T h e test of P. philanthropus h a s b r o w n b a n d s r u n - n i n g d o w n t h e a m b u l a c r a a n d i n t e r a m b u l a c r a , whereas in P. miliaris t h e test is generally green with dark green b a n d s . T h i s difference is probably significant, b u t p e r h a p s t h e present color of t h e fossil speci- m e n s is n o t t h e same as it was originally.

Most previous a u t h o r s h a v e considered Forbes' Echinus ruffini a synonym of P. philanthropus. T h e type (probably in t h e Lyell Collection) c a m e from a locality n e a r Williamsburg, Virginia, w h e r e beds of Yorktown age are k n o w n to occur, a n d a l t h o u g h Forbes' illustrations are n o t very clear, his specimen a p p e a r s to be P. philanthropus.

Cooke ( 1 9 5 9 : 1 6 ) considered P exoletus M c C r a d y a synonym of P. philanthropus; however, t h e type- specimen, w h i c h is lost, was only a small fragment, a n d it is n o t possible from t h e illustration of it to see e n o u g h specific characters to be able to d e t e r m i n e w h e t h e r or n o t it belongs to P. philanthropus. T h e fragment came from " S m i t h ' s , " Goose Creek, South Carolina, from beds t h a t Cooke ( 1 9 4 1 : 1 6 ) considered to be t h e Pliocene W a c c a m a w F o r m a t i o n b u t t h a t later ( 1 9 5 9 : 1 6 ) h e t h o u g h t were late M i o c e n e ( D u - plin M a r l ) .

T Y P E - S P E C I M E N S . — L o c a t i o n of holotype n o t k n o w n ; it is n o t w i t h C o n r a d ' s o t h e r types a t t h e A c a d e m y of N a t u r a l Sciences of P h i l a d e l p h i a ( H . G.

R i c h a r d s , 1971, personal c o m m u n i c a t i o n ) ; figured specimens: U S N M 562264, 559495 (formerly J o h n s H o p k i n s University T 1 0 0 1 ) , U S N M 174450, 1774451, 1774452, 174453, 174454.

STRATIGRAPHIC P O S I T I O N AND GEOGRAPHIC LOCALI- T I E S . — U p p e r M i o c e n e Y o r k t o w n F o r m a t i o n . Vir- ginia: H o l o t y p e from J a m e s R i v e r n e a r Smithfield;

south side of J a m e s R i v e r at J. A. M o g a r t s ' residence 5 miles N of Smithfield, U S N M 166501, collected by W . M . T w i t c h e l l ; Rock W h a r f r o a d on D a y s farm 1.5 miles N E of Smithfield, collected by W . M . T w i t c h e l l ; Bluff W of D a y s Point from u p p e r m o s t

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NUMBER 13 11 bed, James River, USGS 14065, collected by W. C.

Mansfield and C. W. Mumm; Yorktown, USNM 373038, collected by Julia Gardner; 2.5 miles NW of Suffolk, about 0.5 mile below Calhoun Bridge (on right bank of creek), USGS 10198, collected by W.

C. Mansfield. Warren C. Blow collected specimens from his localities 1-4 at USGS 25113, 25114, 25121, 25122. The holotype of Echinus ruffini Forbes came from Burwell's Mill near Williamsburg. All the above localities are probably in Hazel's Orionina vaughani Zone, according to Warren C. Blow (1971, personal communication).

Mellita aclinensis Kier

PLATE 6; PLATE 7: FIGURE 1

Mellita aclinensis Kier, 1963:40-45, figs. 36-41; pi. 15:

figs. 1-3; tbls. 3,4.

Leodia caroliniana Cooke [not Ravenel], 1959:47.

Three specimens are referred to this species, which previously was known from the late Miocene Tamiami Formation in Florida. The Virginia specimens differ only in their larger size. The Florida specimens are less than 73 mm long, whereas the Virginia specimens are 128-147 mm long. Because echinoids commonly occur together in groups of individuals of the same age, the Florida population probably was only more juvenile. The figured Florida specimens have wider lunules, but this is because they are smaller, and in smaller specimens the lunules are wider relative to their length. A larger fragment from Florida is figured herein (Plate 6: figure 3) showing the narrower lunules typical of the larger specimens from Virginia. The dimensions of the Virginia specimens are as follows (in mm) :

Length Width Height

Length of petals:

I I I II I

Width of petals:

I I I II I

Number of porepairs I I I

USNM 174457 128 135 16.0

- - - - 14.2

-

USNM 174458 130 129 12.3 33.0 30.5 38.2 13.1 12.7 12.5 in single poriferous zone of

- ⁸⁸

USNM 174468 147 148 - - - - - - - petals:

-

USNM USNM USNM 174457 174458 174468

II 90 I - 107 -

Width (maximum) of interporiferous zones:

III -

II 4.8 4.7

I 4.1

Distance of apical system from anterior margin:

62.2 60.2 Length of posterior lunule:

26.4 32.2 Distance of peristome from anterior margin:

64.6 62.0 71.0 Considerable evidence suggests that M. aclinensis is the ancestor of M. quinquiesperforata (Leske). The species differ mainly in that M. aclinensis has six lunules and M. quinquiesperforata commonly has five; however, as pointed out by Cerame-Vivas and Gray (1964), some specimens of M. quinquiesperfor- ata have been found with six lunules. Probably the species evolved from the form with six lunules in the late Miocene and Pliocene to a form commonly with five lunules in the Recent. (Two specimens were collected by Richard H. Bailey and Warren C. Blow from Hazel's (1971a) Puriana mesacostalis Zone of the Yorktown Formation at Colerain Landing, North Carolina, which Hazel considers to be early Pliocene.) Although there is a sand dollar, Leodia sexiesper- forata Leske, with six lunules living today off the southeastern United States, I do not believe that it is a descendent of M. aclinensis. The presence of six lunules in Leodia is not really the important morphological character distinguishing Leodia from Mellita.

Cerame-Vivas and Gray (1964) assumed this when they considered that L. sexiesperforata, the type- species of Leodia, should be referred to Mellita.

Leodia sexiesperforata differs from M. quinquiesper- forata, the type-species of Mellita, in having its posterior lunule not extending far anteriorly between the posterior petals, in having its paired interambulacra separated from the basicoronal row by two pairs of ambulacral plates, in having its periproct slightly in- denting the basicoronal plate, and in having a short pair of post-basicoronal plates in the paired interambulacra.

Cooke (1959:47) tentatively referred a specimen from the Yorktown Formation at Days Point to L.

caroliniana (Ravenel), but this specimen is M. aclin- ensis. The test of M. aclinensis is much flatter than

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this South Carolina species, which has a sharper margin, and the lunules are commonly, but not always, narrower.

Although the holotype of L. caroliniana has been lost, there are many specimens in the national collections from localities near the type-locality (Grove Plantation, Cooper River), from beds of the same age and slightly younger, that appear to be conspecific with Ravenel's holotype. These specimens are very variable in the shape of their petals and lunules, and they include specimens that have longer and curved posterior petals with narrow lunules, as in the specimen figured by Ravenel (1842), and the straight posterior petals and short lunules of the specimen figured by Tuomey and Holmes (1857: pi. 1: figs. Aa-c).

Leodia caroliniana should be referred to Mellita not Leodia because the periproct occurs partially within the basicoronal plate (Figure 4 ) , the posterior lunule extends far anteriorly between the posterior petals, the paired interambulacra are separated from the basicoronal row by one pair of ambulacral plates, the

FIGURE 4.—Mellita caroliniana (Ravenel) : plate arrange- ment around the peristome of USNM 174465 from beds considered to be probable late Miocene by Cooke (1959:80)

(X 1.3). Dredged from the Intercoastal Waterway canal 1 to 1.5 miles SW of the bridge on US Highway 17 near Nixon's Crossroads about 15 miles NE of Myrtle Beach, Horry County, South Carolina (collected by L. C. Glenn).

first pair of post-basicoronal plates in the paired interambulacra are elongate, and the lunules are formed by the closing of marginal notches and not by re- sorption of the test. It resembles Encope in its thick test and in the fact that a few specimens have five instead of four genital pores, but the presence of the periproct in the basicoronal plate separates it from Encope, in which the periproct is more posterior and occurs between post-basicoronal plates. Mellita caro- liniana in general appearance strongly resembles the living E. emarginata (Leske), suggesting that Mellita and Encope may have had a common ancestor. This resemblance caused Cooke (1942:20, pi. 3 : figs. 14, 15; 1959:49) to refer these South Carolina specimens, together with a few from North Carolina, to E.

emarginata.

T Y P E - S P E C I M E N S . — H o l o t y p e : USNM 648136;

figured paratypes: USNM 648189-648193; figured specimens: USNM 174457, 174458.

STRATIGRAPHIC POSITION AND LOCALITIES.—Florida:

Tamiami Formation (barnacle-echinoid-oyster facies

= Murdock Station Member of Hunter, 1968:442- 443), spoil banks from group of pits (sec. 29, T. 41 S, R. 23 E) about 1 mile SW of Acline, Charlotte County.

Virginia: Yorktown Formation, Orionina vaugh- ani Zone, at Blow locality 3, USGS 25122; one from Blow's locality 4 (USGS 25121) ; and one specimen in a collection made by G. A. Cooper, J. Cooper, Druid Wilson, and H. B. Roberts; specimen referred to by Cooke (1959:47) probably from same zone at Days Point, James River, W of mouth of Pagan Creek, about 4 miles N of Smithfield, USGS 16920.

North Carolina: Yorktown Formation, Puriana mesacostalis Zone; Colerain Landing, west bank of Chowan River, Bertie County, in a buff, silty sand approximately 100-150 yards S of the Colerain Beach Club, from layer containing Pectin eboreus Conrad, occurring approximately 7 feet above beach level, USGS 25118.

Echinocardium orthonotum (Conrad)

FIGURE 5; PLATE 8: FIGURES 3-7; PLATE 9

Spatangus orthonotus Conrad, 1843b: 327.

Amphidetus orthonotus.—Tuomey and Holmes, 1855: pi. 2:

figs. l-l<r.

Echinocardium orthonotum.—Clark, 1904: 430 [not pi. 119:

figs, la-c, which is Echinocardium marylandiense Kier,

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NUMBER 13 13 new species].—Stefanini, 1912: 706.—Clark and Twitchell,

1915: 213, pi. 97: figs. 2a-c [2a, b with image reversed], pi. 98: figs, la-c [not pi. 98: figs. 2a-c, which is E. mary- landiense Kier, new species].—Cooke, 1942:60.—Cooke,

1959:78 [not pi. 3 3 : figs. 1-5, which are E. marylandiense Kier, new species].

Amphidetus virginianus Forbes in Lyell, 1845a: 425, 2 figs.

Echinocardium virginianum.—Desor, 1858:408.

Amphidetus gothicus Ravenel, 1848:4, figs. 1, 2.—McCrady in Tuomey and Holmes, 1855:7, pi. 3 : figs. 3, 3a-/.

Echinocardium gothicum.—Stefanini, 1912:707.—Clark and Twitchell, 1915:214.—Cooke, 1942:60.—Cooke, 1959:79, pi. 33: figs. 7-10.

Amphidetus ampliflorus McCrady in Tuomey and Holmes, 1855:6, pi. 3 : figs. 2, 2a.

Echinocardium ampliflorus.—Stefanini, 1912:707.

M A T E R I A L . — O v e r 100 specimens, most of which were on a single slab ( P l a t e 9 : figure 3 ) . T h e speci- m e n s lack their spines, b u t , considering their thin, fragile tests, they m u s t h a v e been b u r i e d a t , or soon after, d e a t h . T h e tests a r e a r r a n g e d in h a p h a z a r d fashion, i n d i c a t i n g t h a t they a r e n o t in living position.

T h e description a n d statistics below a r e from 25 specimens from this slab.

S H A P E AND S I Z E . — L a r g e s t specimen 75.0 m m long, smallest 28.3, m e a n 42.8 ( S D 11.5, C V 26.9, N - 2 5 ) ; test wide, w i d t h 8 0 - 9 7 p e r c e n t L, m e a n 86.1 ( S D 3.9, C V 4 . 5 , N - 2 4 ) , greatest w i d t h anterior of c e n t e r ; test high w i t h h e i g h t 4 7 - 6 1 p r e c e n t L , m e a n 53.3 ( S D 4.2, C V 7.8, N - 2 1 ) , greatest height posterior of apical system; posterior t r u n c a t i o n oblique w i t h periproct slightly visible from above.

A P I C A L S Y S T E M . — F o u r genital pores, ethmolytic with genital 2 e x t e n d i n g far posteriorly; located at distance from a n t e r i o r m a r g i n to center of genital pores equal to 4 0 - 5 2 p e r c e n t L, m e a n 45.5 ( S D 2.9, C V 6.4, N - 2 4 ) .

A M B U L A C R A . — A n t e r i o r a m b u l a c r u m n o t petaloid ( P l a t e 9 : figure 1 ) , in groove from apical system to peristome, a t m a r g i n d e p t h of groove equal t o 3.2 p e r c e n t L ; p o r e p a i r s within i n t e r n a l fasciole oblique w i t h a d a p i c a l pore of p a i r larger t h a n a d o r a l , small n o d e b e t w e e n pores of e a c h p a i r ; pores in plates b e - tween i n t e r n a l fasciole a n d phyllode very small, single o r slit-like; 7 o r 8 pores in single poriferous zone from i n t e r n a l fasciole to peristome.

A n t e r i o r p a i r e d petals very wide, with large porepairs outside of i n t e r n a l fasciole a n d 4 - 5 large porepairs w i t h i n i n t e r n a l fasciole in posterior poriferous zones, n o n e in a n t e r i o r poriferous zones within in- t e r n a l fasciole, petals only slightly depressed, n a r -

rowing distally; 1 1 - 1 3 ( m e a n 11.7) large p o r e p a i r s outside of i n t e r n a l fasciole in p e t a l I l a , 7—8 ( m e a n 7.6) large porepairs outside of i n t e r n a l fasciole in petal l i b .

Posterior p a i r e d petals w i t h no large p o r e p a i r s within internal fasciole, 10-12 ( m e a n 11.1) large porepairs in petal V a outside of i n t e r n a l fasciole, 9 - 1 1 ( m e a n 10.5) in petal V b outside of i n t e r n a l fasciole;

o u t e r poriferous zones of a n t e r i o r a n d posterior petals forming almost c o n t i n u o u s a r c ; a m b u l a c r a l plates b e - yond petals with single pores except w i t h i n a n a l fasciole, w h e r e 2 porepairs in e a c h single poriferous zone.

I N T E R A M B U L A C R A . — 2 2 - 2 4 plates in i n t e r a m b u l a - c r u m 5, 15-17 in i n t e r a m b u l a c r u m 1, 13 in 2 from internal fasciole to peristome.

P E R I S T O M E . — L o c a t e d a t distance from a n t e r i o r m a r g i n to a n t e r i o r edge of peristome e q u a l to 2 3 - 3 2 percent L , m e a n 27.5 ( S D 1.8, C V 6.4, N - 2 1 ) ; o p e n - ing w i d e r t h a n high with w i d t h 1 5 - 2 3 percent L, m e a n 19.6 ( S D 2 . 1 , C V 10.6, N - 1 6 ) .

P E R I P R O C T . — L o c a t e d high on posterior t r u n c a t i o n , opening slightly wider t h a n high with w i d t h 16.5 percent L ( S D 2.4, C V 14.7, N - 1 4 ) , height 1 2 - 2 0 p e r - cent L, m e a n 14.6 ( S D 2.5, C V 17.4, N - 1 3 ) ; located between plates 5 - 8 .

O R A L PLATE A R R A N G E M E N T . — L a b r u m w i d e ( F i g - ure 5 ) , extending across almost entire w i d t h of peris- t o m e , e x t e n d i n g very short distance posteriorly, length

FIGURE 5.—Echinocardium orthonotum (Conrad) : Labrum of USNM 174466 from Blow's locality 1 (X 5 ) .

(18)

of l a b r u m 5 - 8 p e r c e n t L, m e a n 6.7 ( S D 0.8, C V 11.9, N - 9 ) ; plastron e x t e n d i n g to posterior m a r g i n , length 5 3 - 6 0 p e r c e n t L , m e a n 57.1 ( S D 1.9, C V 3.3, N - 1 3 ) w i d t h 2 6 - 3 2 p e r c e n t L , m e a n 28.6 ( S D 1.8, C V 6.4, N - 9 ) ; first p l a t e of i n t e r a m b u l a c r a 1, 4 very n a r r o w . A m b u l a c r a w i d e n i n g n e a r peristome, phyllodes with 5 pores in a m b u l a c r u m I I I , 9 - 1 0 in I I , 7 in I.

F A S C I O L E S . — I n t e r n a l fasciole p r o m i n e n t , greatest w i d t h of tract 1.6 m m in specimen 66 m m long or 2.4 percent L, fasciole crossing a m b u l a c r a l plates 7a a n d 7b in a m b u l a c r u m I I I , 1 9 a - 2 0 a a n d 17b in a m - b u l a c r u m I I , 22a a n d 24b in a m b u l a c r u m I, l l a - 1 2 a or b in i n t e r a m b u l a c r u m 5, 8 a - 9 a or b in 1, 7a or 7b in 2 ; greatest w i d t h of a r e a circumscribed by internal fasciole a n t e r i o r of apical system, w i d t h 2 6 - 3 5 percent L, m e a n 30.6 ( S D 2.4, C V 8.1, N - 2 4 ) . S u b a n a l fasciole occurring on posterior t r u n c a t i o n below periproct, area circumscribed by fasciole 15.0 m m wide on specimen 66 m m long or 22 percent L, m a x i m u m w i d t h of tract 1.1 m m wide on specimen 66 m m long or 1.6 p e r c e n t L ; crossing plates 3 - 5 of i n t e r a m b u - l a c r u m 5, plates 6 a - 8 a of a m b u l a c r u m I, plates 6 d - 8 b of a m b u l a c r u m V . A n a l fasciole extending adapically from subanal fasciole ( P l a t e 8 : figure 6 ) .

C O M P A R I S O N W I T H O T H E R S P E C I E S . — T h i s species has been considered in t h e past as including specimens from t h e C h o p t a n k F o r m a t i o n in M a r y l a n d a n d the Y o r k t o w n F o r m a t i o n in Virginia. Cooke ( 1 9 5 9 : 79) noted t h a t t h e r e were some differences between specimens from the two localities a n d suggested t h a t two species m i g h t be represented, b u t h e h a d only two poorly preserved specimens from the Y o r k t o w n a n d could n o t be certain t h a t they were distinct.

Study of a large n u m b e r of specimens n o w available shows clearly t h a t the C h o p t a n k specimens a r e speci- fically distinct from the Y o r k t o w n specimens. A student t test was r u n on dimensions of the two popula- tions, a n d nine dimensions differed very significantly.

T h e s e results are in T a b l e L A P test was r u n to elim- inate all those characters whose variances were too high to p e r m i t a valid t test. Echinocardium orthono- tum differs from E. marylandiense, new species, in h a v i n g a n a r r o w e r , less a n g u l a r , a n d lower test, a n a r - rower a n d less posteriorly situated peristome, wider periproct, longer a n d n a r r o w e r plastron, shorter la- b r u m , n a r r o w e r fascioles, a n a r r o w e r a r e a circumscribed by t h e internal fasciole, a n d less p r o m i n e n t nodes on the i n t e r a m b u l a c r a l plates.

T A B L E 1.—Differences between Echinocardium orthonotum a n d Echinocardium marylandiense

C h a r a c t e r s measured

M e a n percent of length of test

orthonotum marylandiense

Significance of difference by t test (two-sided)

W i d t h of test H e i g h t of test

Distance from anterior edge of peristome to a n t e r i o r m a r g i n W i d t h of peristome

W i d t h of periproct L e n g t h of plastron W i d t h of plastron L e n g t h of l a b r u m

W i d t h of a r e a circumscribed by internal fasciole

86.1 53.3 27.5 19.6 16.5 57.1 28.6 6.7

97.9 59.0 31.6 23.0 12.8 52.0 34.8 9.2

.001 .001 .001 .001 .001 .001 .001 .001

30.7 39.1 .001

R E M A R K S . — E c h i n o c a r d i u m orthonotum a p p e a r s to be a senior synonym of E. gothicum ( R a v e n e l ) from the late Miocene or Pliocene of South Carolina. W h e n only a few specimens of E. orthonotum were available

a n d the variation within the species not k n o w n , E.

orthonotum a p p e a r e d to be distinct from the larger specimens referred to E. gothicum; however, specimens of E. orthonotum now available from Virginia