Cope.] 258 [January 20, 



indulge. On account of the ophidian part of their affinities, I have 

 called this order the Pythonomorpha. 



In time they immediately preceded the Eocene Palaeophides, and 

 probably will find in them structural allies. 



The families embraced are two, the Mosasauridaj and Clidastidse, 

 which differ as follows : — 



The vertebrjE with the zygosphen articulation; the pterygoids free 

 on the internal and external margins; no (?) postparietal arch . . . 



Clidastid^. 

 The vertebras without the zygosphen articulation; the pterygoids 



in contact on the median line; (?) a postparietal arch 



M0SASAURID.E. 



I think it highly probable that the genus Saurospondylus of See- 

 ley, from the lower chalk of England, belongs to this order. If so, it 

 is the type of a peculiar family to be known by the absence of neural 

 spine and low position of the zygapophyses, which have horizontal 

 articular faces. The S. dissimilis Seeley, is a much smaller animal 

 than any here enumerated, and is known by a single vertebra.^ 



Goldfuss states that Mosasaurus possesses a malar arch. This is 

 absent in Clidastes, and I am inclined to doubt whether Goldfuss has 

 demonstrated his point; if present, he states that it is very slender. 



CLIDASTID^. 



Clidastes Cope, Proc. Acad. Nat. Sci. Philad., 1868, p. 233. 



In this genus there has been no trace of hind limbs found. 



Clidastes iguanavus Cope, Proceedings Acad. Nat. Sci, Philad., 

 1868, 181. Ibid. 1869. 



Cretaceous Green-sand of New Jersey. 



Clidastes propython Cope. 



This species is known from an almost complete skeleton found by 

 Dr. Edw. R. Showalter in the Rotten Limestone, near Uniontown in 

 Alabama. 



Its general proportions may be estimated as follows: As a consider- 

 able number of vertebrae have been lost, it will be necessary to 

 illustrate in some points from Cuvier's estimate of the length of Mosa- 

 saurus Camperi. 



1 See Ann. and Mag. Nat. Hist., Sept., 1855. 



