I 
44 EOCENE TESTUDINATA. 
Trionyx leptomitus, Cope. 
Plate xxvi, figs. 1-4. 
Catalogue of Eocene Yertebrata, U. S. Geog. Survs. W. of lOOtb M., 1875, p. 35. 
The costal ridges numerous, close together, and parallel; the hyposternal 
bones pitted, the pits separated by thick ridges or intervals. 
In the typical specimen, the distal end of a costal bone is crossed by 
numerous parallel ribs separated by intervals very little wider than them¬ 
selves, and which inosculate but little. Eleven of these ridges may be 
counted between the broken extremity and the free border. Associated 
with this specimen is a hyposternal bone, which is especially massive, and 
is convex on the inferior face. The twin gomphosial processes are remark¬ 
ably short and stout. A smaller hyposternal bone, collected by A. R. Conk- 
ling, of the expedition of 1875, exhibits the same characters. It is unfortu¬ 
nately not accompanied by carapace. 
A third specimen includes a number of portions of the carapace. The 
middle portions of the costal bones present the usual reticulate pattern, of 
smaller size tlian in the T. radulus, &c., and their distal portions are marked 
with closely-placed parallel ridges, which are frequently connected by 
cross-ribs. The superior layer of the costal bone projects like a roof over 
tlie base of the free j)ortion of the rib. 
Measurements. 
M. 
Thickness of costal of No. 1... 0.010 
Length of fragment of the same... 0.032 
Width of base of twin processes of hyposternal of the same. 0.024 
Thickness of hyposternal of the same. 0.008 
Trionyx cariosus, Cope. 
Plate xxvi, fig. 5-10. 
Systematic Catal. Vert. Eocene, U. S. Geog. Survs. W. of 100th M., 1875, p. 35. 
This is an abundant species in the New Mexican Eocene. While the 
proximal portions of the costal bones exhibit the usual honeycombed 
sculpture, the distal portions, for a considerable length, possess the longitu¬ 
dinal ridges only, or with only occasional connections between them. 
The difference between this species and the T. leptomitus consists in the 
relative remoteness of the ridges, which aiv separated by intervals of two 
