TRIONYCHID.S. 543 



Platypeltis heteroglypta (Cope). 

 Plate 98, fig. 14; plate 101, fig. 2; text-figs. 701, 702. 



Trionyx heteroglyptus, COPE, Proc. Acad. Nat. Sci. Phila. 1873, P- 2 77> U. S. Geol. Surv. Terrs., 

 6th Ann. Report, 1872, (1873), p. 616; Vert. Tert. Form. West, 1884, p. 120, plate xvi, fig. 2. 

 HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 



Platypeltis heteroglyptus, HAY, Amer. Geologist, xxxv, 1905, p. 336. 



The type of this species is the hinder half of a carapace and the complete nuchal bone, 

 which were collected in 1872, by Professor Cope, on the summit of Church Butte, Uinta 

 County, Wyoming., This specimen is now in the American Museum of Natural History, 

 New York, and bears the number 1039. Cope figured it, as above cited, and attempted to 

 restore in outline the missing parts; but, as stated in the explanation of the plate, too few 

 costals are represented. As there restored, the carapace is considerably broader than long, 

 which almost certainly was not the case. Certainly 2, and possibly 3, costals come in front of 

 the most anterior costal present, the fifth one from the rear. In the diagram here presented 

 (fig. 701), the carapace is restored with 7 costals, the number present in the living American 

 species of the family. There is a neural plate between the hindermost costals. These costals 

 may be those of the eighth pair and the neural therefore the eighth; but an eighth neural is 

 so seldom developt (Amyda cequa) that it is more probable that this is the seventh neural and 

 the costals those of the seventh pair. For this reason the species is referred to the American 

 living genus Platypeltis. 



Cope has represented the distal end of the fifth costal from the rear as being drawn in 

 farther than the specimen justifies. In fact, its free margin stood out nearly as far as did that 

 of the next one behind. 



Professor Cope did not know of the nuchal, it having been found, since the specimen came 

 into the American Museum, lying in the matrix beneath the hinder end of the carapace. Its 

 antero-posterior breadth, in the midline, is 26 mm.; its length, from side to side, about 120 mm. 

 It is therefore rather small for a turtle of the size. This nuchal articulated with the first neural 

 and probably with the anterior costals without fontanels. The upper surface is sculptured on 

 the anterior edge for 26 mm. on each side of the midline. Beyond this, the surface is devoid 

 of ornamentation. At the ends of the sculptured area the thickness is 10 mm. The outer ends 

 of the nuchal were partially overlapt by the outer ends of the first pair of costal plates. 



The carapace was possibly quite flat, but more probably it had considerable convexity. 

 There is a narrow, but rather deep notch in the hinder margin of the carapace, at the midline. 

 The measurements given in Cope's description are correct. The greatest width is 250 mm., 

 taken between the distal ends of the fourth pair of costals from the rear. The distance from 

 the rear of the shell to the anterior border of the most anterior costal present is 162 mm. The 

 total length of the shell may be estimated at from 250 mm. to 280 mm. The thickness of a 

 costal plate near its sutural border is 6 mm. The ribs stand out conspicuously on the under 

 side of the plates, and thru them the thickness amounts to 10 mm. Cope states that the free 

 portion of the costal is short. This probably refers to the projection of the rib beyond the 

 plates. The rib of the penultimate costal is present and projects at least 33 mm. The hinder- 

 most pair of costals join along the midline for 25 mm. The neural which is lodged between the 

 front borders of the hindermost costals is 14 mm. long and just as wide. The next neural 

 in front seems to have been 24 mm. long and about 14 mm. wide. Its broader end is 

 directed forward, and its anterior angles come into contact with the antepenultimate costals. 

 A portion of the antepenultimate neural is present and appears to have had about the same 

 width as the ones behind it. Its length was about 25 mm., and it has lain wholly between the 

 costals of the antepenultimate pair, coming into contact with neither the pair in front nor that 

 behind. Its hinder end has been slightly broader than the front end. Only a fragment of the 

 neural next in front of the one just described is present. Its broader end has been directed 

 backward and this has come into contact with the antepenultimate costals. The first neural 

 has had a convex anterior border to fit the concave border of the nuchal. 



The sculpture of the different parts of the shell varies greatly. On the proximal ends of 

 the hindermost costals it is coarse and consists of longitudinal ridges, with some lateral spurs. 

 In the middle of the length of the other costals there is a network of ridges inclosing pits which 



