Smithsonian Contributions to Paleobiology, Number 38, 23 pages, 4 figures, 2 plates, 1978.— Brachiopods from Tertiary and Quaternary sediments of the South Pacific islands are rare. Ladd with the help of local collectors in Fiji and the New Hebrides and members of the United Nations. They were described from Okinawa, where they are associated with Tertiary brachiopods of Japan and the Philippines.
Modern brachiopods occurring in the waters around the above areas are usually closely related to Miocene and later species in the same areas. Interest in these brachiopods will focus on what they can reveal about the conditions under which they lived in the distant past. Lawrence Isham, specialist in visual aids, made the reconstruction of the Dicrosia loop and the outline drawings of Cryptopora.
The ventral valve of Craniscus, unlike that of Crania, is attached only to the apical region, while much of the valve is free from the substrate. The Fijian species is smaller, with almost equal length and width, and generally has a softer folding of the anterior com-. Although the loop of the Fiji species is very narrow for the genus, all other features are in accordance with the criteria for Abyssothyris.
T he extreme thinness and transparency of the shell are characteristics of this genus and abyssal brachiopods in general.
Briggs, Jr
Ventral valve unevenly convex in lateral profile, strongly convex in u m b o, flattened in median region and slightly concave only posterior to anterior border; anterior profile moderately convex; arms with moderate slope. Dorsal valve evenly a n d slightly convex in lateral profile for most of valve length, with anterior part narrowly deflected towards ventral valve; The anterior profile is broadly convex, has short sloping sides and a gentle, narrowly concave median depression. COMPARISON AND DISCUSSION.-This species is quite different from ``Abyssothyris'' elongata Cooper from the Pacific south of Baja California, where it is present in abyssal waters.
This species is about the same size as the Fijian species, but is more narrowly wrinkled and has a more expanded and expanded loop. Elliott (1960) described Abyssothyris from the Miocene-Pliocene strata of Fiji, but this species was found to have a thick median septum not always visible through the shell and other special details of the interior that prevented it from being attributed to Abyssothyris. Dorsal valve with greatest convexity in posterior third; front profile wide and gently convex; anterior two-thirds to half gently swollen.
Dorsal valve with flat o u t e r h i n g e plates not having raised margins formed by crural bases; socket ridges thin. DISCUSSION.-Although a fair number of specimens of this species have been taken, only one is an adult and unfortunately most of the ventral valve is missing. T h i s A t l a n t i c species is more elongated than the Fijian one, but its loop is similar in that it has a narrow and solid transverse and with a strong medial fold.
Argyrotheca SPECIES 1.-This is the largest of the species (USNM 550843), which is nearly equal in length a n d w i d t h . The ventral valve is almost flat and has an anterior valve at the anterior end that fits into a similar one in the dorsal valve formed by a deep and wide sulcus that originates in a midvalve. SPECIES Argyrotheca 3.—This is transversely rectangular in outline with nearly parallel sides and broadly emarginate anteriorly.
The ventral valve has a sulcus originating from about the middle valve, which is occupied by a strong median costa that tends to obliterate it anteriorly. Small, shape variable, ranging from rounded elliptic to transverse elliptic; anterolateral and posterolateral margins rounded; oddly convex, ventral valve irregularly swollen, dorsal valve flattened to slightly concave. Ventral valve medially raised, swelling including umbilical region; side slopes steep; anterior slope rather long, moderately steep.
LOCALITIES.—SM43C (USGS 25652, 25653), SM43D (USGS 25655), USGS 25734
The small specimens show incipient folding characteristic of the genus, i.e. intraplicate, a fold within the dorsal sulcus. Fragments of the posterior of the ventral valve of the small specimens all exhibit well-formed denticles. The young dorsal valves show attachment points of the descending branches of the loop on the median septum.
The loop attachment to the septum is a feature of Fallax, a genus which represents an early arrested stage in the development of Dallina. Although the fragments include young and mature individuals, none of the specimens is a complete valve. Therefore, it is not possible to determine the fold of the anterior commissure, which is usually a useful character in the identification of a terebratelacean.
The posterior portion of the ventral valve has a large round mesothyridial foramen, disjoint deltidial plates and strong tooth plates, important characters of Frenulina. T he ventral side of the cone is shorter than the dorsal side where it is attached to the septum. T he vascula media is strongly entrenched and extends anteriorly from the tips of the diductor scars.
A second thick trunk extends anterolaterally from a point a short distance posterior to the anterior ends of the diductors. One specimen (USNM 550841a), partially filled with calcite, shows the entire loop with its delicate front ring attached to the prongs of the fork. In most of the cleaned specimens, no protruding points or tubercles of the broken descending branches were seen.
Dicrosia is placed in the subfamily Terebratellinae because of its external similarity to other terebratellids, i.e. the presence of strong sulcation which is a characteristic of the subfamily. A revision of the Terebratulidae and Lingulidae, with remarks on and descriptions of some recent forms. Annotated list of the recent Brachiopoda in the collection of the United States National Museum with descriptions of thirty-three new forms.
For synonymy in zoology and paleobiology series, the short form (taxon, author, year:page) should be used, with the full reference at the end of the paper under "Literature Cited". 34; When aligning and arranging elements, follow the format of the series for which the manuscript is intended.
