EOCENE TESTDDINATA. 
59 
The shovel-shaped angle of the left postabdominal, found in connection 
with numerous small fragments, resembles that of H. corsonii in its posterior 
production. It is thinned on the edges, and the extent of that of the inner 
side shows the median notch to have been deep. The roof-like ridge of the 
upper surface is nearer the inner than the external margin, and rises into 
the thickening which bounds the internal abdominal concavity of the plas¬ 
tron in this genus. The inferior surface is uninterrupted, and slightly 
recurved. 
Measurements. 
M. 
Length from the internal marginal thickening.... 0.105 
Tliickness at the internal marginal thickening. . . . .. 0. 021 
Width at the fnndns of the median notch . 0.098 
A second and much smaller specimen may belong to a younger animal, 
or to another species. The posterior border of the postabdominal bone is 
less produced, and the prominent angle is nearer the notch than the line of 
the external border. 
Measurements. 
M. 
Length from the thickening. . 0. 080 
Depth at the same. . . . ... 0.015 
The episternal lip of another specimen is of very large size. The 
greater part of the median sutural border is preserved; but the fracture 
reaches the free border near the base of the lip, so as to leave its extent 
uncertain. It evidently projected decidedly, though not so much as in the 
typical H. corsonii. Its lateral border is not at right angles with the ante¬ 
rior, but passes into it by a bold curve. The inferior face of this portion 
of tlie bone is convex in both directions. 
Measurements. 
M. 
Length of the median suture preserved .. 0.090 
Thickness at the same.. 0.025 
Width at the base' of the lip... 0. 085 
Length to the concavity of the external margin (axial). 0.035 
Thickness of the border of the plastron near the bridge. . 0.037 
The supposed second species is represented by the angular projection of 
the postabdominal of the left side, broken away from the remainder of thebone. 
It presents the external portion of the femoro-anal scutal suture. This frag- . 
ment is characterized by its great thickness and the straight and abrupt 
