540 FOSSIL TURTLES OF NORTH AMERICA. 
this species no plastral bones are mentioned, and in subsequent and more detailed descriptions 
the plastral bones mentioned are not Trionyx-like, we must regard the name P. thomasii as 
belonging to those specimens which were afterward called P. multifoveatus. In the Cope 
collection of reptiles in the American Museum of Natural History there are present the median 
ends of the right and left hyoplastra and a fragment of the left hy poplastron of a trionychid 
which are accompanied by Cope’s labels, which read as follows: : “Plastomenus thomasit, 
hyosternals” and * ‘ Plastomenus thomasit, sternum like Trionyx yx.” The bones bear the number 
1022, of the American Museum. It seems quite certain that thee specimens are the alleged 
types of P. thomasii; but it is quite as certain that they have never been described. A com- 
parison of them with the plastral bones of Bridger specimens of Platypeltis serialis proves 
that all belong to the same species, the oe mance: between the hyoplastra of No. 1022 and 
No. 5944 being very close. 
Platypeltis amnicola Hay. 
Fig. 697. 
Platypeltts amnicola, Hay, Bull. Amer. Mus. Nat. Hist. xxi, 1907, p. 860, pl. liv, figs. 5, 6; 
text-fig. 19. 
The incomplete and fragmentary remains which stand as the type of the present species 
were secured by the Ammetican Museum expedition of 1906 into the Wasatch beds of south- 
western Wyoming. The specimen was found on Bitter Creek. There are present 2 neural 
bones, apparently enough 
oe Fic. 697.—Platypeltis amnicola. Left fragments to restore near- 
<a SS hyoplastron and hypoplastron ly all the costals, most of 
: of type. X2- the hyoplastron and hypo- 
plastron of the left side 
and the inner ends of 
those of the mght side. 
The catalog number is 
6044. 
The carapace had a 
length of about 280 mm. 
and a width of 200 mm. 
or more. The species ap- 
pears to have resembled 
Platy peltis heteroglypta of 
the Bridger beds. 
What is regarded as the 
/ third neural is 35 mm. 
- long, 25 mm. wide, and 
6mm. thick. One costal bone is 46 mm. wide at the distal end, while the sixth of the left 
side is 36 mm. wide distally. The eighth costal of the right side is present. It is small, and 
was evidently inclosed in a notch in the seventh costal. The free ends of all the costals are 
beveled off obliquely. 
There appear to be no welts on the costals. The pits vary considerably in size. Near the 
distal ends the pits are arranged somewhat in rows parallel with the free border, and there are 
usually 6, sometimes 7, in a line 20 mm. long. Toward the proximal ends the pits increase in 
size so as to be two or three times as large as those of the distal ends. They are arranged 
more irregularly also. 
The length of the suture between the hyoplastron and the hypoplastron (fig. 697) seems 
to have been close to 120 mm. The bridge is 45 mm. wide, and here the bones are 13 mm. 
thick. The lower surface of the bones, except the processes, is ornamented with ridges and 
pits. Of the pits there are usually 5 in a line 10 mm. long. 
We may suppose that the plastron of P. heteroglypta resembled that of P. postera. That 
of P. amnicola differs much from that of P. postera, especially in having the anterior border 
of the hyoplastron concave, instead of nearly straight. 
