41)0 FOSSIL TURTLES OF NORTH AMERICA. 



The carapace (plate 90, fig. 1) referred to is nearly complete, wanting only the greater 

 portion of the nuchal; and this was fortunately supplied by another specimen of the same 

 size. The carapace is broader than long, slightly excavated along the anterior border of the 

 nuchal, and truncated behind. The upper surface was rather flat. The total length along the 

 midline is 470 mm.; while the maximum width is 590 mm. 



The nuchal has a length, from side to side, of 290 mm. and a fore-and-aft width of 49 mm. 

 Its anterior border is sinuous, being excavated at the midline; its posterior border is rather 

 strongly convex and it joins the bones behind it without intervening fontanel. There is present 

 a preneural and 6 neurals. The preneural is coffin-shaped, with the broad end forward. Its 

 maximum width is 56 mm. The anterior 5 neurals are also coffin-shaped, but, as usual in 

 trionychids, the narrow end is directed forward. The sixth neural is oval and much reduced. 

 No neural is interposed between the costals of the seventh and eighth pairs; and those of the 

 sixth pair meet behind the sixth neural. The costals of the seventh pair are relatively very 

 narrow, only 36 mm. in the middle of the length. The eighth costals are well developt. The 

 nuchal has a thickness of 18 mm. at the outer end; the first costal is 9 mm. thick at the proximal 

 end and 12 mm. at the distal end. The thickness at the center of the eighth costal is 10 mm. 



The sculpture (plate 88, fig. 6) consists of a network of usually sharply defined ridges 

 which inclose pits of varying size. The ridges are, for the most part, narrower than the 

 diameter of the pits. Toward the distal ends of the costals the pits are more or less transformed 

 into furrows which run parallel with the free border of the carapace. On the hindermost 

 portion of the carapace the pits are unusually large and the ridges are high. Around the whole 

 border of the shell there is a nearly smooth band. This is broadest at the sides of the carapace. 

 On each side of the costal sutures is a band consisting of low ridges which run at right angles 

 with the suture. 



In size, general form, and sculpture, the carapace which has been referred to this species 

 resembles closely that here described as Aspideretes splendidus. The two are, however, 

 different in many ways. A . coalescens has 6 neurals, while A . splendidus has 7. The nuchal 

 of//, coalescens is excavated in front and convex behind, while in A. splendidus it is convex 

 in front and nearly straight behind. The nuchal of the latter has, likewise, a relatively greater 

 lateral extent. The hinder borders of the two species are somewhat different, that of A. 

 splendidus being sinuously convex, with a small median notch, while that of A. coalescens is 

 truncated. In A . coalescens there is not much difference between the width of the proximal 

 and the distal ends of the costals of the first pair, but in A. splendidus the distal ends are much 

 narrower than are the proximal ends. The same statement is true of the seventh costals of 

 the two species. In A . splendidus there does not appear the same tendency toward the for- 

 mation of parallel furrows toward the distal ends of the costals, but rather a tendency toward 

 the production of square cells. 



Aspideretes splendidus sp. nov. 

 Plate 88, figs. 7, 8, 9; plate 91; text-fig. 646. 



Trionyx vagans, .'Cope, Proc. Acad. Nat. Sci. Phila. 1875, p. 9; ?Bull. U. S. Geol. and Geog. Surv. 

 Terrs., in, 1877, p. 573. ?Osborn, Contrib. Canad. Palreont., in, 1902, pp. 12, 16. 



The specimen which is taken as the type of this species is a large, but somewhat imperfect, 

 carapace in the American Museum of Natural History. It is a part of the Cope collection of 

 reptiles, and was collected for Professor Cope in 1876, by Mr. Charles Sternberg, from the 

 Judith River basin, of Montana. It has now the number 3952. The fragments of which the 

 specimen consisted when it came to the American Museum have been put together, and it is 

 now so nearly complete that almost all portions of the carapace can be determined from one 

 side or the other. A slight doubt now exists only with regard to the presence of a preneural 

 and the amount of extension of the ribs beyond the costal borders. 



This species attained a very large size. The width of the type specimen is greater than the 

 length, and the carapace was much deprest. The sides of the carapace are scallopt; there is 

 a slight sinus at the midline behind; and the anterior border formed a gentle curve, with a 

 slight sinus on each side of the midline. 



