264 FOSSIL TURTLES OF NORTH AMERICA. 



It appears probable that the back of this species resembled closely that of Staurotypus tripor- 

 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 

 leftside. 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 I, 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 19 mm.; its height, 27 mm.; its greatest thickness 

 9 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. 9 of the plate cited represents 

 the pygal bone. Its length is 22 mm., its 

 height 1 8 mm., its greatest thickness 8 



FIG. ps.Hoplochelys crassa. Part of right hyoplastron, mm = p erpendicu i a rl v tne outer face is 

 the left hypoplastron, and one left peripheral, probably 



the seventh. X. 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 

 hyohypoplastral suture and near the midline the thickness of the bone is 9 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 Chelydra. The whole 

 arrangement appears to be like that of Staurotypus salvinii, as represented by Dr. Boulenger 

 in his Catalogue of Chelonians. 



