S. W. Williston — North American Plesiosaurs. 227 



in different species of JPolycotylus and Trinacromerum, both 

 relatively short-necked and long-headed plesiosaurs. Much 

 doubt and even ridicule have been thrown upon this supposed 

 habit and the use of the pebbles by these reptiles. But the 

 cumulative testimony of writers, both on this and the- other 

 side of the Atlantic, is quite conclusive. It has been assumed 

 that the plesiosaurs could not have utilized the pebbles as a 

 means of digestion in a muscular stomach. Dr. Eastman, 

 who has vigorously opposed the idea of the possession of such 

 a bird-like structure on the part of the plesiosaurs, seems to 

 have been quite unaware of the fact that the modern croco- 

 diles have a real, bird-like and muscular gizzard, and so 

 described by Dr. Gadow. The crocodiles have a similar habit, 

 or at least such a habit has been imputed to them, and it is 

 not at all unreasonable to suppose that, strange as it may seem, 

 the plesiosaurs had a real, muscular bird-like gizzard, which 

 utilized the pebbles in whatever way the crocodiles may utilize 

 them. 



Elasmosaurus orientalis Cope. Cretaceous of New Jersey. 



This species was based upon two mutilated and isolated 

 cervical centra from New Jersey. It seems far more probable 

 that these vertebrae really belong with Cimoliasaurus. Cope 

 afterwards associated with this species an excellent series of 

 vertebrae from the Pierre of Montana, which I have studied 

 in the American Museum. I have not the least doubt but 

 that Cope was in error in this collocation. I am not sure of 

 the distinction of this specimen from E. platyurus, though a 

 careful comparison of the measurements and sketches made 

 by myself will, I think, decide their identity. If not E. 

 platyurus, the species is doubtless entitled to a new specific 

 name. 



Elasmosaurus intermedins Cope. Fort Pierre Cretaceous of 

 Montana. 



This species was based upon nineteen centra without pro- 

 cesses, and all more or less mutilated ; now in the museum of 

 the Academy of Natural Sciences at Philadelphia. I can not 

 distinguish them specifically from E. platyurus. 



Elasmosaurus serpentinus Cope. Niobrara Cretaceous of 

 Nebraska. 



This species was based upon much better material than was 

 either of the foregoing ones, and it is both recognizable and 

 distinct. Unfortunately, no figures have ever been given of 

 the type specimen, and I have not had, so far, an opportunity to 

 study the specimen. As in his other descriptions, Cope iden- 



