4.6 FOSSIL TURTLES OF NORTH AMERICA. 



rials joining extensively at the midline. Bridge about twice as broad as long. Inframarginals 

 almost wholly on the plastral bones. Plastron with hinder lobe not shortened and not notcht 

 behind. Pelvis not suturally articulated with the plastral bones. Skull pointed anteriorly; 

 most of its surface bones finely tuberculated. Bones of lower jaw smooth; the symphysis 

 short. 



This genus was establisht by Professor Marsh in the year 1890 (Amer. Jour. 

 Sci., XL, p. 177), his type being G. ornatus, collected in the Upper Jurassic of 

 Wyoming. This species is apparently identical with Cope's Compsemys plicatulus. 

 A comparison of specimens of Compsemys victus Leidy with Cope's species just 

 mentioned makes it certain that the two forms are not congeneric. Compsemys 

 plicatulus must therefore be removed from Compsemys, and Marsh's genus Glyptops 

 becomes available. The assignment by Cope of various species of Jurassic and 

 Cretaceous turtles to Compsemys was evidently due principally to supposed resem- 

 blances in the sculpture; but all of these species, except the type, C. victa, must be 

 referred to other genera. There are no evidences that C. victa possest mesoplas- 

 tra. The total absence of distal prolongations of the costals for insertion in the 

 peripherals of C. victa and their presence in G. plicatulus sufficiently separate them 

 generically. 



To Glyptops is provisionally referred G. pervicax, which in some respects 

 approaches more closely Pleurosternon, more especially in having the plastron 

 slightly notcht behind. On the other hand, the bridge is longer than in Glyptops 

 plicatulus. It is not improbable that it represents an undescribed genus. 



It is to be noted that usually when authors have referred to the genus Compsemys 

 they have had in mind the species C. plicatulus, because its characters were well 

 known through Professor Marsh's and Dr. Baur's descriptions; whereas, little is 

 even now known about C. victa. For these references the writer's Bibliography and 

 Catalogue of the Fossil Vertebrata of North America, 1902, p. 437, may be consulted. 



As here employed, Glyptops will include 4 species: the type, G. plicatulus of the 

 Jurassic, G. ccelatus of the Lower Cretaceous, G. pervicax of the Benton, and 

 G. depressus of the uppermost Cretaceous. Possibly when more is known of the two 

 last-mentioned species they will be removed from the genus. 



Glyptops is closely related to Pleurosternon Owen, as already recognized by 

 Dr. Baur. However, it differs from the latter in having the hinder lobe of the 

 plastron less constricted and without posterior notch, in having the inframarginals 

 almost wholly on the plastral bones, in having the costo-marginal sulci well below 

 the costo-peripheral sutures, except over the bridges, and in having longer bridges. 

 The distance from a line joining the free border of the anterior lobe of the plastron 

 w ith the posterior lobe to the outer end of the mesoplastron is contained in the width 

 of the bridge about three times in Pleurosternon and about two times in Glyptops. 



Helochelys is another relative of Glyptops. Its hinder plastral lobe is little more 

 than half as long as w T ide; the plastron appears to have been less closely joined to 

 the carapace than in Glyptops; the bridges are short; and the last neural, the only 

 one known, is hexagonal, with the broader end directed backward. 



Key to the Known Species. 



/. lllT.lssu 



a. Mui rison beds plicatulus 



I I. Cretaceous. 



a. Lowi 1 ( Iretai 1 ous. 



b. Potomac beds ctvlatus 



bb. Benton beds pervicax 



an. I pper Cretaceous. 



c. Denver beds ? depressus 



