and Clavicular Arch in Sauropterygia. 



133 



the characters of the young animal. This inference is supported "by 

 the evidence of the clavicular arch, and by the large size of the 

 radius and tibia as compared with the small size of the ulna and 

 fibula. These bones are not in natural association, being free from 

 matrix ; but I see no reason to doubt that Mr. Leeds has arranged 

 them in positions which are correct. The characters of the skeleton 

 lead to the conclusion that the species is new, and could not become 

 transformed by growth and perfected ossification into any other 

 known species. 



The following are measurements which help to define the species : — 

 Lower jaw, 9 inches. Vertebral column, as preserved and arranged, 

 64 inches. Thirty cervical vertebrae, 23 inches ; two pectoral vertebras 

 supporting ribs on the neural arch and centrum, If inch. Twenty- 

 two dorsal vertebrae measure 22 inches ; three vertebrae in the sacral 

 region, which support ribs, partly on the neural arch and partly 

 on the centrum, 2| inches. Twenty- two caudal vertebrae measure 

 15 inches, but the extremity of the tail is not preserved. The height 

 of the dorsal vetebrae and neural arch is about 2f inches. The trans- 

 verse measurement over the transverse processes of the dorsal 

 vertebrae is 4^ inches. The longest dorsal ribs measure about 

 9 inches. The ilium is 4 inches long. The transverse width over the 

 pelvic articulation is 7|- inches. The antero-posterior extent of the 

 pelvis is 9 inches. The pubis measures 4|- inches from front to 

 back. The ischium is inches in the same measurement toward the 

 median line. The pelvic foramina were separated from each other by 

 cartilage. The femur is 8 inches long and 4 inches wide. The 

 coracoid is 7 inches long by 4^ inches wide ; the scapula is 4J inches 

 in length and width. These shoulder girdle bones are exceptionally 

 thick. The transverse width over the two clavicles is 1\ inches. 



The clavicles are thin triangular bones, perfectly ossified, with 

 sharp well-defined margins and no signs of immaturity, probably 

 because they are membrane bones. If they met each other in the 



Fig. 5. — Clavicles of a young individual Plesiosaurus durobrivensis. 



