Cope.] 260 [January 20, 



MOSASAURID^. 



There are probably three generic forms known in this group. We 

 know them to differ so far, only in their vertebrae and mode of im- 

 plantation of teeth, though no doubt others exist. As to distinguish- 

 ing them by the crowns of their teeth, I doubt the possibility of this, 

 not only in this family, but even in any of the order, so far as known. 

 They are, in this respect, like the serpents, whose genera cannot be 

 distinguished in peculiarities of the solid teeth onlyj 



The dorsal vertebrje compressed, the body elongate 



Macrosaurus. 



The dorsal vertebrae more or less depressed; the articular faces 

 transversely ovate; pterygoid teeth in alveoli Mosasaurus. 



Vertebrae as the last ; the pterygoid teeth pleurodont 



Platecarpus. 



The species which have been described appear to be referable to 

 the above genera, as follows: 



IMacrosaurus Owen. 



Tliis genus has undoubted relationships to Clidastes; I have ob- 

 served in a few of its vertebrae traces of a notch which, in the latter, 

 separates the zygosphen from the zygapophysis. Unfortunately other 

 portion? of the genus are unknown. 



Macrosaurus validus Cope. sp. nov, Nectoportheus validus 

 Cope, Proc. Acad. Nat. Sei. Philad., 1868, 181. 



Cretaceous Green-sand of New Jersey. 



Macrosaurus laevis Owen, Quart. Joum. Geol. Society, Lon- 

 don, 1849, V, 380. 



Cretaceous Green-sand of New Jersey and ? North Carolina. 



Mosasaurus Conybeare. 



There are numerous species of this genus which appear to belong to 

 two groups, the one characterized by the rounded, and the other by 

 the depressed form of the lumbar vertebras. A species of the latter 

 type has been referred to the genus Amphorosteus by Gibbes. They, 

 however, seem to graduate into each other in such a way as to pre- 

 clude generic distinction on that ground. 



The giants of the order belong here, for the M. missuriensis, M. 



