EOCENE TESTUDINATA. 
45 
and three times their width. The superior layer of the costal bones is 
produced far beyond the inferior or costal portion, causing a deep longitu¬ 
dinal grooving of the free border of the carapace. At the sutures, the pits 
are lengthened so as to continue across them, there resulting an unreticulated 
band extending on each side of each suture. 
In a large specimen represented by many fragments, the postabdominal 
bone is thicker than any of the costals, and presents a rather short free 
margin round its lateral extremities. Its surface is simply honeycombed. 
The hyposternal of the first specimen is flat, and presents a rather 
irregular reticulate sculpture medially. 
Measurements. 
M. 
Thickness of distal end of first costal. No. 1. 0.011 
Length of overhanging free edge of first costal. No. 1... 0.012 
Thickness of postabdominal bone. No. 2 .. . 0.015 
Antero posterior width of postabdominal bone, No. 2. 0.046 
Thickness of a costal bone medially... 0.012 
Thickness of another costal bone proximally... 0.007 
Width of another costal bone proximally. .. 0.042 
AA.—The superficial part of the costal bones not overhanging, but obliquely contin¬ 
uous with the free rib-extremity : 
Trionyx radulus, Cope, 
Plate xxvi, figs. 11-16. 
Loc. cit., p. 35. 
This turtle is nearly allied to the T. cariosus. As in it, the proximal 
portions of the costal bones and the vertebral bones are honeycombed, 
while the distal parts of the former are parallel-ribbed. Five to nine of 
these ribs can be counted from the free end. They are not closely placed, 
being narrower than their intervals. The size of the species is the same as 
that of T. cariosus, but the costal bones are more uniformly thinner. 
Measurements. 
M. 
Width of a costal bone. No. 1..... 0.044 
Thickness of a costal bone. No. 1. 0.006 
Width of a vertebral bone, No. 1.. 0.029 
Trionyx ventricosus, Cope. 
Plate xxvi, figs. 17-23. 
Represented by portions of three individuals from the collections of 
