the Cretaceous and Tertiary Formations. 457 



J witli large osseous shields, symmetrically arranged, and 

 waaraeated, resembling in this respect tlie modern Helo- 

 Otlier parts of the body, especially the ventral region, 

 Dtected by rectangular, ' orn'^mented shields, united to 

 t'ler by suture, and, in some of the species, these were 

 '. The teeth are pleurodont, and, in the species in which 

 ' ' preserved, are round, with obtuse summits, not unlike 

 ; Trachydosaurus rugosus Gray, from Australia. The fron- 

 i\v, especially in front, a distinct median suture, which 

 slightly obtuse angle with their posterior margin. The 

 ;!• bone projects behind the cotylus far backward and 

 ird, resembling in this respect the corresponding part in 

 "^' Niloticus. The dorsal and caudal vertebra3 have the 

 - Mieral form as those of Varanus^ but show traces of a 

 lione articulation, especially in their rudimentary zygan- 

 -Mties. The tail was long, and apparently rounded. Some 

 "I' 'he species were larger than any existing American lizards. 



The known species of the present genus may be distinguished 

 fn.^m Saniva ensidens Leidy,* by the teeth, which in the latter 

 are compressed, pointed, and have sharp cutting edges. There 

 i>. moreover, no evidence that this hzard had osseous dermal 



L of the cranial shields 

 ^vill perhaps afford the most convenient and satisfactory char- 

 acters for distinguishing the species represented in the present 

 collection of lacertian remains, which, although numerous, are 

 more or less fragmentary. The present species may therefore 

 be characterized as having, on the frontals between the orbits, 

 shields of moderate thickness, but little elevated, with those in 

 tne middle row on each frontal broader than long. Each shield 

 ^ covered with numerous small polished tubercles, crowded 

 together with no definite arrangement. Ventral shields with 

 the same ornamentation were found with some remains of this 

 *Pecies, and probably belong with them. 



\rl u!^ ^i ^!"Sle frontal, at posterior margin, V'SO lines. 



;\>'lth of single frontal, between orbits, 5-30 " 



-eugth of five posterior shields on middle row of frontal, 9' 



lln^tK ^I ^^^gi^e^t of jaw bearing three teeth, . . 4-10 " 



Will ^l ^'^"tral shield, probably of this species, 8-40 " 



^^Jdthof the same....... .. - 4-75 " 



whl P^mf ^^ specimens indicate a reptile about four feet in 

 f^ph. They were discovered by Mr. C. T. Ballard and the 

 sam k'^^ ^nzzly Buttes, near Fort Bridger, Wyoming, m the 

 ^ ne beds that contained the Crocodilian remains. 



* Proceedinga Philadelphia Acad. Nat. Sciences, 1870, p. 124. 

 J 005. Sci.-Third Series, Vol. I, No. 6.-June, 1871. 



