120 THE WASATCU AND liKlDGEU FAUN^. 



ridges are always wider and more obtuse than in T. scutumantiquum and 

 T. uintaensia. 



I did not obtain the last-named species in Wyoming, so far as I know, 

 and I refer to Dr. Leidy's work for a full description of it and of the T. 

 guttatus. 



Trionyx heteroglyptus Cope. 



Annual Report U. S. Geol. Surv. Terrs., 1872 (1873), p. C16. 

 Plate XVI, fig. 2. 



Carapace broad, flat, concavely truncate behind. Free portion of costal 

 bones short. The last pair of costal bones are in contact by a common suture 

 by about two-thirds their width, the anterior portion being separated by the 

 last vertebral bone. There is a great diflference between the sculpture of 

 the middle of the carapace and its lateral portions. The former region is 

 coarsely ribbed longitudinally, the intervening grooves being mostly unin- 

 terrupted. On the middle portions of the costals the ridges are more or 

 less broken up, and distally they are very delicate, forming an inosculating 

 pattern, inclosing small pits. On the last costal they retain their ridge-like 

 character. The posterior vertebrals are marked by a single groove down 



their middle. 



Mea«uremenU. 



M. 



Width of (■■ara])ace at antepenultimate cost.al bone 235 



Length from front of carapace at autepenultimato costal bone backwards 095 



Width of car-ajHice at antepenult iniate costal distally 048 



Length of last two vertebrals 037 



This is a handsome species, and appears to be rare, as I have but two 

 specimens that I can definitely refer to it. It is, however, difficult to dis- 

 tinguish separated ends of costal bones from those of T. guttatus. I dug one 

 of the specimens from the summit of the Church Butte, Wyoming. 



Trionyx concentricus Cope. 



Proceed. Amer. Philos. Soc, 1872, p. 469 (published July 29). 

 Plate XVI, figs. 3-6. 



This species reposes on various fragments, in one case representing 

 numerous poitions of a carapace. The sculpture is intermediate between 

 those of T. hderoglyptm and T. guttatus. The costals have subequal and 



subruund pits throughout the entire length of the bones, but their inter- 

 8 o 



