AND AVKS OF NORTH AMERICA. 



211 



POLYGONODON RECTUS. Emmons. 

 Mosa.taurus rectus, Emmons, Geological Survey, N. Ca., 1858, 218. Polygonodon rectus, Emmons, 1. o. tab. 



Emmons found his specimen in the miocene in North Carolina, but considered it an 

 intrusive fossil from the Cretaceous. The present survey under Prof. Kerr has a similar 

 specimen also from the Miocene. 



Miocene of Bladen and Duplin Counties, North Carolina. 



CLIDASTIDyU. 

 CLIDASTES, Cope. 

 Proceedings Academy Nat, Sci., Phil., 1808, p. 288. 



This genus was originally established on a species represented by a single dorsal ver- 

 tebra, but its characters have been chiefly developed from remains of two other species, 

 especially the nearly complete skeleton of the C. propython. The vertebra is highly 

 characteristic, and resembles considerably that of such genera of Iguanidee as Eupbryne 

 and Dipsosaurus, and in some degree those of Cyclura and Iguana. It differs from the 

 dorsals of known serpents in having the zygosphen on the plane of the anterior zygapo- 

 physis, and in having the costal articular surface continuous with and covering the diapo- 

 pbyses. It differs from the genera of Iguanidee mentioned, in the very small amount of 

 upward direction which the face of the articular ball of the centrum exhibits. 



The zygapophyscs arc spread apart, and their outer margin continues in a straight 

 line from the diapophyses. The diapophyses are directed upwards, and are vertical com- 

 pressed in form ; they are opposite to about equal portions of the centrum and neural 

 arch. Their posterior face is slightly concave, and the upper face behind forms, with the 

 neural arch, a deeply concave line. The convexity of the ball is not so great as in the 

 Crocodilia, and with the thin-lipped cup, resembles that of Mosasaurus ; this resemblance is 

 heightened by the slightly depressed upper outline of the ball, and the form of the 

 diapophyses. 



The genus is most nearly allied to Liodon, in some of the vertebra of which a slight- 

 groove beside the zygapophysis is the rudiment of the zygantrum. 



The premaxillary is a narrow, simple element, one-half of a cone anteriorly, and much 

 attenuated posteriorly, separating the maxillaries above, by width of its spine only. Its 

 extremity projects considerably beyond the latter, and its sides are only bevelled to receive 

 them, there being no sutural connection. The spine terminates a short distance beyond 

 the anterior margin of the nares. The anterior extremity bears two teeth on each side, 

 which are smaller than the larger maxillaries. 



The maxillary bones are long and slender, and widely separated on the palatal sur- 



