500 



FOSSIL TURTLES OF NORTH AMERICA. 



The carapace (plate 94, fig. i) of the type of this species had a length of 330 mm. and a 

 breadth of 263 mm., not including the extension of the ribs beyond the costal plates. If we 

 include the ribs, the width was at least as great as the length. 



The nuchal is a considerable bone, having had an extension from side to side of about 

 175 mm., and a width of about 35 mm. at the midline. Anteriorly it is somewhat excavated, 

 while posteriorly it is articulated with the preneural. It was not in contact with the anterior 

 costal plates, but its distal extremity probably overlapt the distal end of the rib of the first 

 costal. The connection of the nuchal with the bones behind it was, therefore, a rather loose 

 one. In Bell's Monograph of the Testudinata there is a figure (plate liv) of Trionyx labiatus 

 (TestuJo triunguis Forskal) which shows a nuchal much like that of the fossil species 

 here described. The living species differs, however, from A. puercensis in not having the 

 nuchal articulated to either a costal plate or a median bone, only overlapping the ends of the 

 ribs projecting from the first costal plates. 



The nuchal of//, puercensis is thin, except for a rib-like thickening which follows the length 

 of the bone on the lower side. The lateral wings terminated in digitations. On the upper side 

 the bone is smooth and was covered with soft tissue, except a patch in the midline, 48 mm. 

 from side to side and 25 mm. fore and aft. This has the sculptured surface found elsewhere 



on the carapace. Around this area, 

 on the sides and behind, the bone 

 is beveled off in continuation with 

 the beveling of the edge of the rest 

 of the carapace. 



Between the proximal ends of 

 the first costals we find 2 bones, a 

 preneural and the first neural. 

 The former is irregularly penta- 

 gonal, with the broadest side artic- 

 ulating with the nuchal. The two 

 shortest sides lie in a notch of the 

 first neural. The anterior 5neurals 

 are elongated hexagonal, with the 



FIG. 656. Aspideretes singularis. X 4. Carapace of type. 



broadest end directed posteriorly. The next neural is quadrilateral, while the last is nearly 

 triangular. The dimensions of the preneural and the neurals are given in the table. 



The first costal is the broadest of all. In front and laterally it is beveled off from the 

 sculptured layer to the inner surface. Medially it articulates with the preneural and with the 

 long side of the first neural. The width of the succeeding costals diminishes toward the rear. 



The thickness of the costals is pretty uniformly 7 mm. near the sutural borders, and 9 mm. 

 thru the rib. The latter extended beyond the edge of the costal plates for a considerable 

 distance; in the case of the rib of the second costal, somewhat more than 50 mm. The ribs 

 are broad, occupying about half the width of the costal plates. 



Of the plastron (plate 104, figs 2,3; text-fig. 655) there are present the left hyoplastron, 

 the left hypoplastron, and part of the right xiphiplastron. These elements do not differ in any 

 important respect from the same bones in living Trionychidae. Altho they are quite thick, 

 they are not unusually large. The width of the hyoplastron and the hypoplastron taken 

 together, measured across the narrowest part, is 55 mm.; and of this width each occupies one- 



