616 GEOLOGICAL SURVEY OF THE TERRITORIES. 



thin, and exhibits the peculiar decussating pattern of lines of deposition 

 characteristic of the same layer of the dermal scuta of Crocodilians. 

 jS'o portions were obtained which can with certainty be referred to the 

 carapace. The ilium is short, stout, and recurved, and the pubis is 

 largely expanded. 



AXBSTUS BYSSINUS, Cope. 

 Loc. cit. 



The procoracoid and scapula are of equal lengths, and the coracoidis 

 much dilated distally. 



The portions of the plastron preserved are thin for the size of the 

 animal, and all the bones are dense and smooth. The postabdominal has 

 the free margins acute and senulate. There is an external gently con- 

 vex edge, with a long process extending backward, and one long, nar- 

 row one inward. The enamel is white, and is marked with decussating 

 lines of osseous deposit, as in woven linen. This is not the result of 

 weaving. The cervical vertebra is without spine ; it is not pressed in 

 the middle, and is without any pneumatic foramen. 



Measiiremeiits. 



M. 



Length cervical vertebra 0. 068 



Diameter at middle 020 



Diameter at end 035 



Diameter caudal end at ball 010 



Length Olo 



Length of an ungual phalange 043 



Proximal depth ungual phaUmge 013 



Length postabdonunal, (broken) 180 



Width postabdominal •. 120 



Locality of the last. 



TEIONYX, Geoffr. 



Trionyx hetero&lyptus, Cope, sp. nov. 



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

 costal bones short. The last pair of costal bones are in contact by a com- 

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

 separated by the last vertebral bone. There is a great cliifereuce be- 

 tween the sculpture of the middle of the carapace and its lateral por- 

 tions. The former region is coarsely ribbed longitudinally, the inter- 

 vening grooves being mostly uninterrupted. 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. 



Measurements. 



M. 



Width of carapace at antepenultimate costal bone 0. 235 



Length from front of carapace backward 095 



Width of carapace, costal, distally 048 



Lengt]| of last two vertebrals 037 



Excavated from the Bridger bed, on the summit of Church Butte, by 

 the writer. 



