TRIONYCHID. 541 
Platypeltis trepida Hay. 
Fig. 698. 
Platypeltts trepida, Hay, Bull. Amer. Mus. Nat. Hist. xxi, 1907, pl. liv, fg. 7; text-hg. 20 
The single known specimen of this species was found by the American Museum expedition 
of 1906 into ihe 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 
ee ea ae neurals except the fourth and the fifth. 
1 22 agi 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 g2 
mm. Beyond this the ribs extended at 
least 15 mm. 
The fourth neural is 11 mm. long and 
g 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 2mm. The first is 16 mm. wide; the 
second is 12 mm. wide at the distal end. 
a7 
GS Br ., ty The anterior border of the first shows that 
LS 4 a ~ B 
oi ; Se a it was articulated by a jagged suture with 
\ pac 
(om eae <\ 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. serralis. 
Fic. 698.—Platy peltts tre pida. @aeapace of type. X 3. 
Platypeltis trionychoides (Cope). 
Plate 110, figs. 1-2; text-figs. 699, 700. 
Anostira trionychoides, Copr, Proc. Amer. Philos. Soc., xu, 1872, p. 461. 
Plastomenus trionyc hordes: Core, Proc. Acad. Nat. Sci. Phila. oa p- 279; Ann. Report U. S. Geol. 
Surv. Wyoming, etc., 1872 (1873), p. 619; Vert. Tert. Form. West, 1884, p. 123, plate xvii, fig. 1.— 
Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 453. 
Pyatypeliis trionychoides, Hay, Amer. Geologist, XXXV, 1905, p. 336. 
Professor Cope originally referred the present species to the genus 4nosterra, a proceeding 
due, as he tells us, to the fact that the type specimens were found commingled with various 
bones of Anosterra 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 ort bones, bearing Cope’s label stating that they are 
type specimens, are in the Anierican 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. 1 and 2 of plate 110 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 
