264 FOSSIL TURTLES OF NORTH AMERICA. 
It appears probable that the back of this species resembled closely that of Staurotypus tri por- 
catus, as represented on plate xxB of Gray’s Catalogue of Shield Reptiles. 
None of the peripheral bones at hand show that there was a dentated suture between them 
and the costals. Those which articulated with the plastron are thick and heavy. Of these 
there were probably 5 on each side. Plate 38, figs. 4, 5, represents one which is regarded as 
the sixth peripheral of the right side. It is slightly larger than the corresponding one of the 
left side. The length is 22 mm.; the thickness of the hinder end, 17 mm.; that of the anterior 
end, 10 mm. The outer surface is strongly convex, and furnisht with a longitudinal sharp 
ridge. The anterior portion of the inner surface is concave. Along the lower border of this 
face are three excavations for digitations from the hypoplastron. Near the upper border is a 
deep cylindrical pit for the extremity of a rib. The hindermost digitation of the hypoplastron 
has evidently past on to the next peripheral behind, probably the seventh. Other thickened 
peripherals present almost certainly belonged farther forward and received the digitations of 
the hyoplastron. Between these and the thickened peripheral just described there was at 
least 1, probably 2, thinner peripherals. One of these, the fourth or the fifth, is represented 
by figs. 6 and 7 of plate 38. Its length is Ig mm.; its height, 27 mm.; its greatest thickness 
g mm. _ Its outer surface is convex perpendicularly, and is traverst by the continuation of the 
ridge described as occurring on the thickened peripherals. The inner surface is concave 
perpendicularly. In the upper half of this face is a pit for a rib-end; near the lower border 
are 3 shallow pits for digitations from the plastral bones. The lower edge was connected 
with the plastron by a dentate suture. 
This bone or one similar to it was con- 
nected partly with the hyoplastron, 
partly with the hypoplastron. Each of 
these peripherals is traverst by a perpen- 
dicular sulcus. Along the upper border 
runs a longitudinal sulcus and along the 
lower border another, all these forming 
the boundaries of the marginal scutes. 
Fig. g of the plate cited represents 
the pygal bone. Its length is 22 mm., its 
height 18 mm., its greatest thickness 8 
mm. Perpendicularly the outer face 1s 
concave, the inner strongly convex. It 
is doubtful whether the upper border 
formed a jagged suture with the suprapygal. Another free peripheral, probably the tenth, 
resembles the pygal in general features. 
Text-fig. 325 represents the left hypoplastron attacht to the seventh peripheral. Near the 
hyohy poplastral suture and near the midline the thickness of the bone is g mm.; at the outer 
extremity the thickness is 4 mm. At the narrowest portion the width is 11 mm. The 
bone was united with the one on the opposite side by a coarse suture; similarly with the 
xiphiplastron. With the thicker peripherals it was articulated by means of digitations; 
with the intermediate and thinner ones, by both digitations and dentated sutures. A pro- 
cess of the xiphiplastron extended along the outer, hinder angle of the hypoplastron. 
On the lower surface, between the outer and the middle thirds of the bone there is seen 
a shallow sulcus, the inner boundary of an inframarginal scute. Another sulcus begins 
at the inguinal notch and runs forward and inward to the meeting of the transverse and 
longitudinal sutures. 
On the left side of the figure last cited is represented the outer two-thirds of the hyoplas- 
tron of the right side. At the narrowest part the bone was 16.5 mm. wide. The bridge was, 
therefore, at its narrowest portion, about 27 mm. wide. On the outer end of the bone are sulci 
bounding portions of 2 inframarginal scutes. No other sulcus is seen on this bone; and it is 
not probable that there was one beginning at the axillary notch and running backward and 
inward to meet the one from the inguinal notch, such as we find in C helydra. The whole 
arrangement appears to be like that of Staurotypus salvini1, as represented by Dr. Boulenger 
in his, Catalogue of Chelonians. 
Fic. 325—Hoplochelys crassa. Part of right hyoplastron, 
the left hypoplastron, and one left peripheral, probably 
the seventh. 3. 
