53S FOSSIL TURTLES OF NORTH AMERICA. 



deposits of New Mexico. His figures represent fragments of 3 costal plates. He states that 

 the species is readily distinguisht bv the closely placed suhparallel ridges which cross the ribs 

 parallel to the axis of the body and which are separated bv one or two rows of imprest dots, 

 or small fossae. 



The costals varied in width from 18 mm. to 27 mm. and in thickness from 3 mm. to 5 

 mm. Three and a halt ridges occupied a space of 9 mm. 



The American Museum of Natural History expedition of 1903 to the Bridger beds in the 

 region about Fort Bridger, Wyoming, secured a large portion of the carapace and a consider- 

 able part of the plastron of a specimen which it appears necessary to refer to Cope's Wasatch 

 species. When, however, more satisfactory materials of the latter have been secured, it may 

 prove that the Bridger remains belong to an unnamed species. 



Cope's assignment of his materials to the genus Plastomenus depended on no part of the 

 plastron, and was therefore inconclusive. There is reason to believe that the Bridger speci- 

 men does not belong to Plastomenus, but must be assigned to Platypeltis. It bears the cata- 

 log number 6014. 



Of the individual here described (plate 98, fig. 13) there are present most of the first 

 neural and the whole of the third; practically all of the 6 anterior costal plates, and a fragment 

 of the seventh; the mesial half of the right hyoplastron and hvpoplastron; and somewhat more 

 of the mesial half of the same bones of the left side. 



It is evident that the nuchal of this individual had no sutural connection with the costals 

 of the anterior pair; whether or not it had such connection with the first neural is made doubt- 

 ful by the fact that the anterior portion of this bone is missing. The hinder border of the 

 carapace being gone, as well as the nuchal, the length can not be determined. From the front 

 of the first costal to the hinder border of the sixth is 95 mm. |udgingfrom the curve of the tree 

 borders ol the sixth costals, but a few millimeters, perhaps 10 mm., would have been added 

 by the seventh costals. If now we add 10 mm. as the width of the nuchal, we shall have as 

 the probable length of the carapace 105 mm. The width of the disk is 100 mm. How far the 

 ribs projected beyond the disk can not be determined. 



The first neural had a length of about 16 mm. and a width of 13 mm. The third has the 

 same length, but is 12 mm. wide. Both are of hexagonal form, with the narrow end directed 

 forward. The sixth neural was also of the same form, but had the narrow end directed back- 

 ward. There was present a small seventh neural wedged in between the costals of the sixth 

 and seventh pairs. 



The third costals are 17 mm. wide near their outer ends, 3.5 mm. thick near the sutural 

 borders, and 5 mm. thru the rib. Toward the outer ends of the costals the ribs become quite 

 prominent on the inner surfaces of the former. 



The ornamentation of the carapace agrees with that of Cope's Plastomenus senalis. 

 There are on each side about 7 longitudinal ridges, or welts. These are low on the front of the 

 shell but much more prominent posteriorly. Five of these ridges cross the sixth costal. Be- 

 tween the ridges there are from 1 to 3 rows of pits of varying sizes. On the neurals there are 

 only small pits, or punctae. 



1 be plastron of this specimen, so far as represented, was like that of Platypeltis spimfera. 

 1 he width oi the hyoplastron (plate 109, fig. 3), where narrowest, is 7 mm.; that of the hvpo- 

 plastron at the same place, is 10 mm. The inner end of the former bone expanded into a 

 single flat process; that of the hypoplastron into two such processes. A callosity of 15 mm. 

 width occupied these bones along their common suture, about half of it on each bone. 



No. 5944 of the American Museum of Natural History, a specimen collected at Grizzly 

 Buttes, Wyoming, in 1903, is referred to this species. It consists of portions of the carapace, 

 the right hyoplastron and hypoplastron nearly complete, the median halves of the same bones 

 of the left side, portions of the pectoral and pelvic girdles, and parts of the humerus and femur. 

 These belonged to an older and larger individual than the one just described. The carapace 

 (plate [09, fig. 4) is remarkable for the strong development of the longitudinal ridges; but it 

 is not believed that a distinct species is indicated. One fragment belongs to the hinder rim 

 of the carapace, and presents the seventh and eighth costals of the right side. The eighth 

 costal was small. I he plastron (plate 109, fig. 2; text-fig. 694) is in a more advanct stage of 



