TRIONYCHID^:. 



541 



FIG. 698. Platypfltis trepida. Carapace of type. X 



Platypeltis trepida Hay. 



Fig. 698. 

 Platypeltis trepida, Hay, Bull. Amer. Mus. Nat. Hist, xxm, 1907, pi. liv, fig. J; text-fig. 20. 



The single known specimen of this species was found by the American Museum expedition 



of 1906 into the Bridger beds of southwestern Wyoming. It was secured at Grizzly Buttes in 



the level designated as B. The catalog number is 5925. 



The nuchal bone is wanting, as well as most of the costals of the right side and all the 



neurals except the fourth and the fifth. 

 The original length of the specimen was 

 close to 100 mm. The distance from the 

 anterior border of the first costal to the 

 hinder border of the fifth at its distal end 

 is 77 mm. The breadth of the disk is 92 

 mm. Beyond this the ribs extended at 

 least 15 mm. 



The fourth neural is 1 1 mm. long and 

 9 mm. wide. The fifth is 10 mm. long and 

 8 mm. wide. Each of these bones bears 

 a low median keel. 



The costals are thin, the thickness being 

 about 2 mm. The first is 16 mm. wide; the 

 second is 12 mm. wide at the distal end. 

 The anterior border of the first shows that 

 it was articulated by a jagged suture with 

 the nuchal bone. The costals show some 

 faint traces of longitudinal welts. The pits 

 are mostly arranged in rows parallel with 



these more prominent ridges. There are from 5 to 7 pits in a line 10 mm. long. 



The closer connection of the nuchal with the first costals, the finer sculpture, and the keel 



on the neurals distinguish this species from P. senahs. 



Platypeltis trionychoides (Cope). 

 Plate no, figs. 1-2; text-figs. 699, 700. 



Anostira trionychoides, COPE, Proc. Amer. Philos. Soc., xn, 1872, p. 461. 



Plastomenus trionychoides, COPE, Proc. Acad. Nat. Sci. Phila. 1873, p. 279; Ann. Report U. S. Geol. 



Surv. Wyoming, etc., 1872 (1873), p. 619; Vert. Tert. Form. West, 1884, p. 123, plate xviii, fig. I. 



HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 453. 

 Platypeltis trionychoides, HAY, Amer. Geologist, xxxv, 1905, p. 336. 



Professor Cope originally referred the present species to the genus Anostcira, a proceeding 

 due, as he tells us, to the fact that the type specimens were found commingled with various 

 bones of Anosteira ornata and all were supposed to belong to one species. When the error was 

 discovered, the trionychoid bones were assigned to Plastomenus. The character of the sculp- 

 ture doubtless determined this distribution of the species, for it does not appear that Cope 

 possest any of the plastron. Cope's figured specimens of his species are now in the U. S. 

 National Museum, but fragments of costal bones, bearing Cope's label stating that they are 

 type specimens, are in the American Museum of Natural History. They are in all probability 

 portions of the type which have become separated from the figured specimens. All of Cope's 

 specimens of the species came from Cottonwood Creek, Wyoming, and hence from the level 

 known as B. 



Figs. I and 2 of plate 1 10 are reproduced from photographs of a nearly complete specimen 

 of the species which was obtained by the American Museum expedition of 1903 into the Bad- 

 lands of southwestern Wyoming. This specimen, which furnishes, besides the carapace, a 

 large part of the plastron, both humeri, and both femora, was found at Grizzly Buttes. The 

 number of the specimen in the American Museum is 5938. The length of the carapace along 



