PAIRED FIN GIRDLES. 



Pectoral Fin. 



Supracleithrum. — In position almost parallel to the 

 axis of the body; a round shaft anteriorly, but becoming 

 wider and dorsoventrally depressed posteriorly; articu- 

 lates at its rounded anterior end by fibrous tissue with 

 the concavity on the posterior surface of the laterally 

 directed wings of the pterotic. The posterior portion of 

 the supracleithrum overlies and articulates by fibrous 

 tissue with the dorsolateral surface of the cleithrum and 

 postcleithrum. 



Cleithrum. — Wide dorsally, but tapering to a 

 narrow shaft in the lower third of its length; much ex- 

 panded posterolaterally throughout the middle of its 

 length. The cleithrum articulates by fibrous tissue dor- 

 sally with the overlying supracleithrum and with the 

 anterior half of the ventral edge of the postcleithrum, 

 which it overlies. Posterodorsally the cleithrum articu- 

 lates by fibrous tissue and slight interdigitation with the 

 anterior edge of the scapula. Along its posterior edge, in 

 about the middle of its length, the cleithrum articulates 

 by fibrous tissue with the anterodorsal and antero- 

 ventral edges of the coracoid. The anterior ends of the 

 two cleithra articulate with each other by fibrous tissue 

 in the midventral line of the body between the medial 

 edges of the platelike portions of the first branchiostegal 

 rays at the level of the end of the ceratohyal. 



Postcleithrum. — A rounded shaft anteriorly, but 

 becoming compressed posteriorly into a thin sheet whose 

 outline is highly irregular from specimen to specimen. In 

 none of the specimens is there any evidence of two 

 separate elements making up the postcleithrum, for the 

 dorsal and ventral postcleithra apparently have fused 

 into one piece. The postcleithrum articulates by fibrous 

 tissue anteriorly with the cleithrum and supra- 

 cleithrum. 



Coracoid. — Constricted in the middle, but 

 expanded dorsally and even more expanded ventrally; 

 cartilage filled along its dorsal and anteroventral edges; 

 articulates by fibrous tissue anterodorsal ly and antero- 

 ventrally with the cleithrum, while dorsally it articu- 

 lates through cartilage with the base of the scapula and 

 bases of the second to fourth actinosts. 



Scapula. — Scapular foramen not entirely enclosed 

 by the scapula, but, rather, with the lower half of its 

 anterior edge closed by the cleithrum; cartilage filled at 

 its dorsal and ventral edges; articulates by interdigi- 

 tation anteriorly with the cleithrum, posterodorsally 

 with the anterior edge of the first actinost and postero- 

 ventrally with the anteroventral edge of the second ac- 

 tinost. Ventrally the scapula is supported through car- 

 tilage by the coracoid. 



Actinosts. — Four elements; all cartilage filled at 

 both ends, except for the reduced first actinost, which is 

 cartilage filled only dorsally; first actinost a triangular 

 wedge interdigitating with the dorsal half of the poste- 

 rior edge of the scapula and the anterodorsal edge of the 

 second actinost; second, third, and fourth actinosts more 

 or less constricted in the middle, but with decreasing 

 amounts of constriction from the second to the fourth. 

 The second, third, and fourth actinosts interdigitate with 

 one another at their ventral edges of contact, and the 

 anteroventral edge of the second actinDst interdigitates 

 with the posteroventral edge of the scapula. Dorsally the 

 first, second, and third actinosts interdigitate with one 

 another. The fourth actinost articulates anterodorsally 

 with the third actinost by fibrous tissue in some 

 specimens but by interdigitation in others. The second to 

 fourth actinosts are supported basally through cartilage 

 by the coracoid. Distally the actinosts and scapula sup- 

 port by fibrous tissue most of the fin rays. 



Fin rays. — Twenty-two to twenty-four fin rays 

 present in most specimens; the first ray very small and 

 divided into two halves throughout its length, the medial 

 half much larger than the lateral half. The first ray ar- 

 ticulates by fibrous tissue with the scapula, whereas the 

 other rays articulate with the actinosts. The first two 

 rays and the last ray are unbranched; all the others are 

 branched. Fiist ray without cross-striations, the others 

 cross-striated. 



VERTEBRAL COLUMN. —All vertebrae with 

 biconcave centra, except for the last, which ends poste- 

 riorly in fusion with the parhypural and hypurals. 



Abdominal Vertebrae. 



First vertebra. — Neural spine bifid; neural arch 

 with a bony roof over the neural canal, the shelflike 

 medial processes from each side of the neural arch 

 meeting and interdigitating in the midline; articulates 

 by fibrous tissue over the upper half of the anterolateral 

 surface of its centrum with the short exoccipital con- 

 dyles, while the rim of the concave anterior end of the 

 centrum rests against the rim of the concave posterior 

 end of the basioccipital. The deeply concave postero- 

 lateral edge of the neural arch articulates by fibrous tis- 

 sue with the anteriorly projecting neural prezygapophy- 

 sis of the second vertebra. 



Other abdominal vertebrae. — Twelve abdominal 

 vertebrae in 10 specimens. The 1st to the Uth ab- 

 dominal vertebrae have bifid and divergent neural 

 spines. The bifid neural spines are of about the same 

 height on all the vertebrae, but the anteroposterior 

 length of the spines increases from the 1st to about the 

 4th abdominal vertebra and then decreases from the 5th 

 to the 11th abdominal vertebra. Shelflike medial projec- 

 tions from each side of the neural arch meet and inter- 

 digitate (or even fuse) in the midline to form the bony 



