482 FOSSIL TURTLES OF NORTH AMERICA. 
Cope did not clearly distinguish this species from P. edemius. One last costal is indeed 
mentioned as being crost by longitudinal ridges; and he states that if these had been broken 
up into tubercles Ke would have referred the specimen to P. wdemuus. 
In the collection of turtles secured by the American Museum expedition of 1903 there are 
2 specimens which the writer refers to P. molopinus. These were obtained at Grizzly Buttes, 
from the level known as B. One of these, No. 5941, presents a practically complete carapace 
and a few fragments of the plastron; the other, No. 5945, consists of a portion of the carapace 
and some parts of the plastron. These remains show great resemblances to P. edemius, and 
it is possible that they should be referred there, and that P. molopinus is not different from 
the former species. There is, however, one difference between the two forms which appears 
to be constant. This is found in the ornamentation of the outer surfaces. Little if any differ- 
ence is to be seen in the character of the welts, but the pits, or puncte, of P. molopinus are 
smaller and closer together than they are in P. wdemius. In the latter there are usually only 
3 or 4 pits in a space of 10 mm.; while in P. molopinus there are quite constantly 6 or 7, 
occasionally but 5. To the eye, the sculpture of the 
latter has a much finer appearance. In the case of both 
cee species, the longitudinal welts are broken up, on the last 
. costals, into elongated tubercles. It is also to be noted 
S that the pits and puncte of P. molopinus are more gen- 
erally distributed over the carapace than they are in 
(ey \ PR edemius. 
_| In P. edemius the neurals, the proximal ends of 
4 most of the costals, and the whole of the hindermost cos- 
tals, are smooth or nearly so, except where varied by 
> ine = the presence of welts. _ 
ne The sculpture on No. 5941 is not very distinct, a 
—/ fact that is due principally to the dirty color of the speci- 
aa | men. No. 5945 is of a clear sage-green and has been 
| ; weathered free from all matrix. It shows the welts and 
— the puncte with great distinctness. 
A No. 5941 (plate 85, fig. 3; text-fig. 642) has a length 
a of 200 mm. and a width of 180 mm. It resembles closely 
| eA the specimen, No. 5978, which has been described here 
a er oe as P. wdemius. It was, in life, evidently quite convex. 
It differs from P. wdemius, as represented by No. 597 
in having the costals of the sixth pair wholly separated 
by the sixth neural. No. 5945 differs from No. 5978 in 
the same way; but it differs from No. 5941 in having 
a minute seventh neural. This neural is regarded as having no specific value. No. 5945 
further differs from No. 5941 in the somewhat broader neurals, and in having the free 
borders of the costals less abruptly beveled. 
Of both specimens, No. 5941 and No. 5945, the mesial end of the hyoplastron is present. 
It differs from the same region in P. edemius in having a notch in the front border, mesiad 
of the process against which the outer end of the entoplastron rests; but whether or not this 
might appear with greater age is uncertain. The distal end of the hypoplastron is present in 
No. 5945. It differs somewhat from that of P. edemius, but it is impossible to say how con- 
stant this difference is likely to be. 
The sculpture of the plastron differs from that of the plastron of P. @demrus in consisting 
ot smaller and more closely placed pits and puncte. Of course, in making the comparison 
corresponding regions must be compared. 
Both the specimens here referred to P. molopinus were secured in the Bridger beds of the 
western end of Grizzly Buttes. Cope figures specimens from the Wasatch of New Mexico 
under the name P. communis. These are indicated in the text (Wheeler Surv., Iv, p. 50) as 
‘var. i,” but in the explanation of plate xxv as “‘var. i.” We must be uncertain about this 
identification until additional materials of the supposed molopinus have been secured in the 
Wasatch beds. 
Fic. 642. —Plastomenus molopinus. 
Carapace. X 4. No.5941 A.M.N.H. 
