228 FOSSIL TURTLES OF NORTH AMERICA. 



single narrow inguinal. We see, therefore, that, excepting the axillary and the inguinal scutes, 

 there were no inframarginals. This conclusion is confirmed by the more complete shell of 

 Basilemys sinuosa Riggs. 



Of the elements of the carapace the nuchal is unknown and but little is known of the neu- 

 rals. With the type are parts of 2 costals. One of these appears to be the eighth of the right 

 side. The length of the fragment is 144 mm.; its width was at least 56 mm. At the middle 

 of the width the thickness is 13 mm. The borders and the course of the rib on the inferior 

 surface show that the costal was curved backward from its proximal to its distal end. Not far 

 from its hinder border it is traverst by a deep dermal sulcus. The position of the other costal 

 fragment can not be determined. 



Of the peripherals there are present an anterior one, probably the second, the lower halves 

 of most of those forming the bridge on the right side, and those of the right side from the 

 inguinal notch to the pygal. In the collection of the Canadian Survey the third right peripheral 

 is represented by the portion bounding the axillary notch. The greater part of the pygal is 

 with Cope's type. Therefore, with the exception of the nuchal, one anterior peripheral, and 

 the outer halves of the bridge peripherals, we are acquainted with the whole rim of the carapace. 



The anterior peripherals did not project so far beyond the soft parts of the animal as did 

 the posterior. The supposed second projected beyond the soft skin of the under side 52 mm. 

 Its length along the free border is 90 mm. The thickness is 21 mm. The portion which articu- 

 lated with the first costal is missing. The upper surface of the bone is nearly flat; the lower 

 is somewhat convex; the free border is acute. 



The third peripheral, as represented by the Canadian specimen, has the thinner portion 

 which articulated with the first costal broken away. The sutural edge which joined the outer 

 anterior angle of the hyoplastron is present. On the anterior end of the outer surface is a 

 right-angled ridge, which farther forward passes into the sharp free border of the carapace. 

 Below this ridge the sculptured surface lookt downward toward the axillary notch; the surface 

 above the ridge was a part of the upper surface of the shell. The whole length of the bone is 

 about 90 mm. and its greatest thickness is 38 mm. 



The figure shows what parts of the various bridge peripherals are present. Probably just 

 beyond the line of fracture the peripherals curved upward to join the lower ends of the costals. 

 This outer, or upper, portion of these bridge peripherals appears to be represented by one bone 

 in the Cope collection. The costal margin of this bone was about 18 mm. thick and this 

 border is nearly straight. The length of this peripheral is 103 mm. and it rises at least 1 10 mm. 

 The sculpture of the outer surface is not so coarse as on most of the bones. 



The seventh peripheral (plate 34, fig. i), the one entering into the inguinal notch, is thick 

 and heavy. Its length is 82 mm.; its thickness anteriorly, 44 mm., posteriorly, 20 mm.; its 

 height, at least 70 mm. Its free border is rounded in the middle of the length, becoming 

 broader and flatter anteriorly, sharper posteriorly. The figure just referred to shows the 

 details of the sculpture. The next four peripherals have respectively the lengths too mm., 87 

 mm., 62 mm., and 53 mm. The heights vary from at least too mm. in the eighth to 75 mm. in 

 the eleventh. The upper border of all appears to be broken away, but the suture evidently was 

 near. The eighth, ninth, and tenth have their outer surfaces somewhat concave from above 

 downward, so that these have a slight upward flare. A fragment of the pygal has on it the 

 descending sulcus, thus showing that the bone was about 60 mm. wide. Its free border is 

 acute and the bone is 18 mm. thick, 70 mm. above the free border. 



The connection of the costals with some of these posterior peripherals is interesting. It is 

 well shown in an eighth right peripheral in the Canadian collection. This is broken so as to 

 show that the end of the rib beyond the costal plate extends downward into the substance of 

 the peripheral about 30 mm., forming a gomphosial articulation. No such articulation is seen 

 in the bridge peripheral above described. 



The greater portion of the pygal is present in the type of the species. It had a length of 

 60 mm. along the free border and a height of about 75 mm. The outer surface is nearly flat, 

 the inner convex. The free border is acute, as is that of most of the peripherals. 



So far as can be determined, the sulci between the costal and the marginal scutes followed 

 pretty closely the sutures between the costal and the peripheral plates. No sulci are found 

 crossing the two costal plates present. On the eighth and ninth peripherals a deeply imprest 



