46 
EOCENE TESTUDINATA. 
1874 and 1875 respectively. The sculpture of the carapace of these differs 
from that of the other species in consisting everywhere of close and rather 
fine vermiform ridges, which are frequently interrupted, and as frequently 
inosculate. Some of the associated fragments have a tubercular appearance, 
while others are reticulate in a small pattern. The accompanying hypo- 
sternal bone is characterized by its downward convexity and the thickness 
of its external free border. The twin gomphosial processes are short and 
stout. The sculpture is in parallel wrinkles, which inosculate sometimes, 
and are sometimes interrupted. 
While this species approaches slightly the Trionyx leptomitus in the 
sculpture of the distal part of the costal bones, and the form of the hypo- 
sternals, it may readily be distinguished by the totally different sculpture of 
the latter, and of the proximal part of the costals, and by the beveled edge 
of the superficial layer of the carapace, which does not overhang the free 
end of the rib. 
Measurements. 
M. 
Width of a costal bone proximally....... 0.025 
Thickness of a costal bone..... 0.007 
Thickness of a costal bone distally......... 0.008 
Thickness of a hyposternal bone distally... 0.008 
This species is smaller than the others, but very stout. 
II.—The pitted sculpture of the costal bones extending to their ends: 
Trionyx guttatus, Leidy. 
Trionyx guttatus, Leidy, Report U. S. Geol. Surv. Terrs. (4to), p. 176, pi. ix, fig. 1. 
T. uintaensis, Leidy, Cope, Syst. Catal. Vert. Eocene New Mexico, U. S. Geog. Survs. W. 
of 100th M., p. 35 (not of Leidy). 
The distinguishing character of this species is expressed in the above 
definition of section II. To it must be added that the distal ends of the 
costal bones are beveled regularly to the free rib-extremity. 
Almost the entire carapace of one of the individuals of this species was 
obtained by myself. The pitting is uniform and without interruption, 
extending even to the sutural edges of costal bones. It is strong on the 
vertebral bones, but, near the distal ends of the costals, becomes obscure; the 
border itself being smooth. The ribs separating the pits are coarse, but not 
so wide as the pits. From the suture of the first costal, it is evident that 
