Medium-sized body, expanding quite rapidly from the column to the apex of the first radial Fs, where it is about one-fourth wider than high. Body small, slightly cupped, broad below and slightly expanded above; about twice as wide as the top of the first radials.
148 PROCEEDINGS OF THE ACADEMY OF
First anal piece about one-third as large as one of the subradials, hexagonal in shape, and resting between the upper sloping sides of two of the subradials, and partly under one side of one of the first radials on the right; while it supports another anal piece above, and is connected with a third on the left side, which. Subradial pieces that curve inward into the cavity of the base and extend outward around the column; all show an almost pentagonal overall outline, with short lateral edges, except that on the anal side, which appears hexagonal (each with no visible corner in the center of the underside). Second radials as wide as the first and almost twice as long, all pentagonal in shape, with the upper angle projecting and also projecting outward, while a strongly defined mesial angle extends through the center of the dorsal or outer side to the base of each corner, the surface on each side of this corner being clearly concave.
The anal parts are small and due to the wide surface of the plates, and the distinctness of the sutures, without clearly defined outlines. As can be made out, the first appears to be somewhat cuneiform, and embedded in the slope under one side of the first ray on the right; on the left it connects above the middle, apparently with another resting on a very short upper side of one of the subradials.
150 PROCEEDINGS OF THE ACADEMY OF
Subradial small tumid, abruptly curving into the "concavity" of the underside and extending about halfway up the side walls of the body; three or four pentagonal and one or two on the anal side hexagonal (not counting the obtuse angle which doubtless exists in the middle of the lower side of each). The other radials are as wide at the base as the first, and nearly twice as long, each pentagonal forming and supporting two arms, except that of the anterior set, which is quadrangular and supports only one arm; each with a distinct, well-defined, sharp carina extending up the middle, and the dorsal surface on each side of this carina distinctly concave. The arms (except in the anterior ray) first split at a sixth above their origin on the other radials, at whereby the inner part is somewhat smaller than the other, and simple to the end, while the outer splits again into a seventh part above, and a third time at an eighth part above the latter, the inner divisions being all simple.
On comparison with the original typical specimen of this species, but now before, it appears that the species under consideration differs in having its second secondary piece, each provided with a sharp, strongly defined mesial carina, and the surface of each side of the carina distinctly coucave, instead of having these pieces only obtuse round.
152 PEOCEEDINGS OF THE ACADEMY OF
153This species is related to Potcriocrbws hursxformis, white, which has This species is related to Potcriocrbws hursxformis, white, which has. The specimens are not in condition to show much of the ventral prolongation, but one of them shows it to be very nearly as long as the arms, and somewhat expanded, and crowned with short spines on the upper limbs. We readily observed that in some of their characters they corresponded most closely to Slrotocrimis, and in others they appeared more allied to Actinocrinites, and at the same time we were very much inclined to think that a strictly systematic definition of all the various genera of Crinoidea would require their separation as a distinct intermediate genus.
Since that time we have had the opportunity of studying an extensive number of these and the allied groups in Mr. Wachsmuth's collection, and have been led to the conclusion that if this type does not form a separate genus, occupying an intermediate position between Strotocrinus and Actinocrinites , ^hviiits should be placed as a separate subgenus.
154 PROCEEDINGS OF THE ACADEMY OF
The base is much depressed, or about four times as wide as high, broadly truncated, and only slightly concave below; The margin is extended more or less horizontally and deeply notched at the sutures. Anal tracts unknown above second range; first one smaller (especially pillar) than the first radians, and supporting two others of its own size in the next range. Interradial pieces three to five in each space; the first is as large as the second radians, hexagonal in shape, and bears on the upper sloping sides two smaller pieces, above which are generally one or two small pieces.
The single piece below and the first above each section is thin, rounded, and more or less tapering, and generally two or three wedge-shaped pieces follow the latter before beginning a double series of alternating pieces, above which the arms are somewhat broad and moderately long. The surface of all the body plates is deeply convex at the corners and accentuated in the middle, the prominence of the first radials usually forming a transverse ridge, from which a single more or less defined vertical ridge ascends the other radials to the middle of the third, whence it splits. - cate and continue to the secondary radials.
156 PROCEEDINGS OF THE ACADEMY OF
Base about twice and a half as wide as high, not thickened or expanded below, and but very slightly notched at the sutures; facet for the reception of the column large and moderately concave, with fairly large central perforation. Second radials barely half as large as the first, about as wide as they are long, quadrilateral, pentagonal, or unequally six-sided. First interradial pieces, about half the size of the first radials, heptagonal, and supporting two smaller pieces in the second range, above which there are one or two even smaller pieces in the third, and a small piece over the last, sandwiched between the brachial pieces.
In the structure of its body, as well as in the formula of the wing, this species agrees with Actinocrinusclavus^ of Hall. For this group we propose the name Pkysetocrinus (^Da-xToc, swollen; xpivov,a . lily, allusion to the ventricose vault of the typical species, Act. ventricosus, Hall.)t.
NATURAL SCIENCES OF PHILADELPHIA. 159
160 PROCEEDINGS OF THE ACADEMY OF
It appears to have about the same connection with section (b) of the genus Stroioc7-inus as the subgenus Physetocrimts with the typical forms of Strotocrimts. The first piece is as long as the first radials, but narrower, heptagonal in shape, and supports one small piece above its middle and a larger piece on each upper inclined side in the second area; in the third set there are three, in the fourth two pieces, and above these three smaller pieces extending upwards to connect with the arch. The first interradials are about the size of the third radials, hexagonal, and bear two smaller pieces in the second set, above which are some five or six very small, irregular pieces, some of the upper ones extending upward and connecting with the arch.
From the underside of this transverse ridge, two or three others extend down to the first radial and the first posterior part, so as to connect with the other basal parts. The second and third radial pieces each have about three small pointed nodes arranged transversely, while from the third radial narrow ridges extend to the secondary radials and then in branches to the base of each arm.
34;162 PROCEEDINGS OF THE ACADEMY OP
In the number and arrangement of the pieces composing the walls of the body, up to and including the third radial pieces, this genus presents no essential differences from Actinocrinus, with which it also agrees in having the bases of the arms more or less grouped, or separated by interradial and anal spaces, and never around a continuous, as in £ f nor an ex])anded disc, asin Strotocrinus. It differs, however, not only from Actinocrinus proper, but the general physiognomy and the nature and position of the opening, but especially in the fact that its arms are composed of a double series of alternating pieces of all the bifurcations, as in Amphoracriiius, of which however, it is very different in other respects. This peculiarity of the arms being each composed of a double series of alternating pieces below as well as above the bifurcations, is not only continued into the body, but some species have each division of the rays forming part of the walls of the body is included, the same structure almost a quarter of the way down the side. within one or two pieces of the third primary radials.
Hall's Wtiilei species; but being larger and more robust, its body-plates are more convex, and without the ridge extending up the radial series of the \Vliite> species, which also differs in some other particulars, and comes from the upper part of the Burlington beds, and ours from the lower, while only any species of Crinoids are believed to be common 1869.].
164 PROCEEDINGS OF THE ACADEMY OF
NATURAL
166 PROCEEDINGS OF THE ACADEMY OF
First radial pieces that extend beyond horizontally from the end of the column, exposing a flat hexagonal surface almost twice as wide as long. Thirdials wet, or distinctly projecting beyond the surface of the second and first; wider than long, larger than these second, and pentagonal hexagonal inform; each influence on its own. In the posterior rays the intermediate brachial pieces are interposed between the others, so as to give origin in each of these rays to three arms, making twelve arms to the whole series.
The first anal piece is as wide as long, heptagonal, with a cutting surface entirely contained in the concavity of the underside, supporting in the next three pieces, which are longer than/side, and arcing upwards in a lobe form from the outer wall, but not included in concavity of the lower surface. In connection with the outer end of each of these are two oblong narrow pieces in the other area, which are usually moist at the lower end and extend up between the arm-pieces to connect with the vault.
168 PROCEEDINGS OF THE ACADEMY OP
169This species is related to Platycrinus Aviericamis, from Owen and Slmraard. This species is related to Platycrinus Aviericamis, of Owen and Slmraard, with which it agrees in the size and shape of its body. Wachsmuth finds specimens exactly corresponding to the species of Owen and Shumard in the ornamentation of the body, and yet having only six arms per ray, or thirty in the whole series, instead of eight toes per ray, as is contemplated. Similar differences are also seen in the details of the other divisions, while the surface decoration of the two species is entirely different, and the base of the Wortheni is flat or broadly concave, rather than moderately convex with only a central concavity.
The disk of this species is circular in outline, slightly convex above, and measures from 0-20 to 0-30 inches in diameter. Impressions of the upper side of the slender arms show that they have been somewhat rounded above, with the almost square arm pieces slightly alternating.
170 PROCEEDINGS OF THE ACADEMY OP
MOLLUSCA
The hinge line is scarcely more than one-fourth the maximum length of the shell, measured obliquely from the anterior extremity to the posterior basal margin, and runs at an angle of about 45° to the longer axis of the valves. A surface with concentric lines is unclear; the ray side of the posterior dorsal region is very faintly marked and wider than the slight furrows between them, while in some very indistinct traces of fine longitudinal furrows may be visible; radiating cost88 of the front, fine and rather sharply defined on the gaping margin, on the back of which may be seen some larger indistinct ribs, the last of which is larger than the others, and curves down from the front of the beak, so as to intersect the margin of the valve a little below the lower end hiatus. Shell medium size, longitudinally elongated, length more than twice as long as height, very thin, rather convex in central and umbilical region .. anterior margin rather short, closed and narrowly rounded; basal margin forming a long, almost semi-elliptical curve, with a very slight sinuosity before the middle; posterior sidecompressed; but apparently a little gaping and markedly truncate, almost vertical, from base about halfway up and thence somewhat obliquely forward and upward to dorsal margin; posterior dorsal region compressed on crest of ubona; cardinal margin equal to about two-thirds of the whole length of the shell, very nearly a strand, and bent so as to form a narrow lanceolate linear bodice extending its whole length; . beaks convex, rising a little above the cardinal margin, and placed a little more than one-sixth the length of the forelimb valves;
Surface ornamented by about twenty-five very regularly arranged, distinctly raised conttric costa*, beginning near the lunate, and extending backward, parallel to the base, to the well-defined, angular ural)onal ridge, which of the beaks leading to the posterior basal extremity, which becomes a sharp or sole skirt. very nearly so, is chiefly represented in the more compressed posterior dorsal region by distinct lines of growth, crossed in the middle of this area by a second oblique ridge extending from the bill to the middle of the posterior margin.
