536 FOSSIL TURTLES OF NORTH AMERICA. 



Ilie sculpture of the carapace was of moderate coarseness. On the distal halves ot the 

 costals the pits are in rows parallel with the free border of the costal, and there are five of these 

 rows in a line 20 mm. long. Proximally the pits are no longer in rows and are larger, 3 or 4 

 in the distance named. The sutural borders of the costals are striated across the sutures. 



Fig. 690 represents the known bones of the plastron. A portion of the hyoplastron is miss- 

 ing, but it is quite certain that the outer end has been placed very close to its proper position. 

 This bone had an extent laterally of about 252 mm., not including the antero-external spine. 

 It is remarkable for the narrowness of the end next the midline, this being only 60 mm. The 

 width at the bridge was about 52 mm. The greatest thickness ot the bone is about 17 mm. 

 The outer end of the hypoplastron is wanting, as well as the hinder border of the bone. The 

 bottom of the notch receiving the inner process of the xiphiplastron is present, so that the form 

 of the hypoplastron given in the drawing is not far from correct. The width at the narrowest 

 part of the bridge is 37 mm., being thus less than that of the hyoplastron. The thickness at 

 the bridge is 21 mm. 



On account of the advanct age ot the individual, the layer of the bone forming the 

 "callosities" extended itself to the ends of the processes at the midline. The lower surface of the 

 plastral bones is nearly smooth, but shows everywhere the vestiges of pits and ridges. Where 

 distinct enough to be perceived they seem to have been smaller than those of the carapace. 



The sculpture ot the carapace of this species resembles that of Amyda uintaensis, consisting 

 of large pits at the proximal end ot each costal and somewhat smaller ones in rows at the distal 

 end. Those of T. manducans are, however, somewhat larger, in corresponding situations. 

 The shell, too, is thicker. The greatest differences are found in the plastra of the two species. 

 In A. uintaensis the inner end of the hyoplastron is two and a half times as wide as the nar- 

 rowest portion at the bridge; whereas, in T. manducans the two portions are ot nearly the 

 same width. The front border ot A . uintaensis was quite concave, while that of T . manducans 

 was nearly straight. It is not probable that such differences can be due to difference in age. 

 The type of A . uintaensis is about four-fifths as large as that of the present species. 



From Amyda scutumantiquum the present species differs in the same way that it does 

 horn A. uintaensis; that is, in the narrowness of the inner end of the hyoplastron. A. radula, 

 whose nuchal has a similar thickened anterior border, differs in having a thinner shell, the 

 free borders of which are beveled, and in having a finer sculpture. A. egregia has a thicker 

 shell, a coarser sculpture, and no overhanging layer at the free borders. A.? cariosa, of the 

 Wasatch of New Mexico, evidently had much deeper and more abrupt pits on the proximal 

 ends of the costals. The bone regarded by Cope as a xiphiplastral was deeply pitted, a con- 

 dition not to be expected in T. manducans. Aspideretes guttatus has a different sculpture 

 and a relatively broader bridge. Aspideretes ellipticus had a nuchal whose anterior border 

 was beveled oft on the upper surface. 



Genus PLATYPELTIS Fitzinger. 



Carapace with the eighth pair of costals wanting or greatly reduced. No preneural. One 

 or two of the posterior pairs of costals may be in contact on the midline, or all may be separated. 

 ^ 1 Ming in the living species with smooth or granulate skin. 



The type of the genus Platypeltis is Testudo fcrox Schneider {=Trionyx ferox ot Boulen- 

 ger's Catalogue). The known living species are all inhabitants of North America. 



Key to Fossil Species of I'latypeltis. 



A 1 , l'ucrco or Torrejon species: 



I. Nuchal probably loosely attacht to first costals. No welts on carapace. Six pits 



in a line 10 mm. long antiqua 



A". Wasatch species: 



1. Disk ot carapace not as wide as long; with ribs projecting far beyond disk. 



Nuchal probably loosely connected with its costals and neural; sculpture coarse, 



with welts serialis 



2. Sculpture" coarse, especiall) on proximal ends of the costals, hut without wilts. 



Anterior bordei ol hyoplastron concave amnicola 



A 3 . Bridger species: 



1 . See A 2 , 1 set talis 



2. Nuchal sutured to hist mst.ils, welts not conspicuous; $ to 7 pits in 10 mm.... trepida 



