AND AVES OF NORTH AMERICA. 47 



This genus is well distinguished from Plesiosaurus by the peculiarity of the scapular 

 arch. The mesosternum appears to be coossified with the claviculi, and the three ele- 

 ments form a broad breast-plate. If the claviculus was ever united with the scapula as in 

 Plesiosaurus, no evidence of it can be seen in the specimen. Both the clavicular and me- 

 sosternal elements are broader and more extended anteriorly. 



The American genera of Elasmosauridae may be compared as follows : 



Posterior cervical vertebrae without diapophyses: cervicals longer, compressed, neck 



very elongate. 



Elasmosaurus. 



Posterior cervical vertebrae with diapophyses : cervicals quadrate, shorter, depressed, 

 rapidly diminishing in size, hence the neck shorter. 



ClMOLIASAURUS. 



Prof. Owen figures and describes (Reptiles of the Cretaceous, Palaeontogr. Soc.) a 

 vertebra which very closely resembles the cervical of Elasmosaurus. He considers it to 

 be the cervical of a peculiar Plesiosaurus, which he calls P. constrictus, remarking, at 

 the same time, its remarkably inferior pleurapophyses. This I believe to be a species of 

 Elasmosaurus or an ally, and to be called for the present Elasmosaurus constrictus. 



ELASMOSAURUS PLATYURUS, Cope. 



Leconte's Notes loo. cit. Proceed. Acad Nat. Sci., 1868, 1. c. 92. 

 Discosaurua carinatus, Cope. Leconte's Notes, 1. c. 



This, after Mosasaurus the most elongate of the sea saurians yet discovered, is represented by a more than 

 usually complete skeleton in the Museum of the Academy of Natural Sciences in this city. It was found by Dr. 

 Theophilus H. Turner, the physician of the garrison at Fort Wallace, a point situated 300 miles westward from 

 Leavenworth on the Missouri river, and some distance north from the Smoky Hill Fork of the Platte river. Portions 

 of two vertebras presented by him to Dr. Leconte when on his geological tour in the interest of the IT. S. Pacific 

 Railroad Company, were brought by the latter gentleman to the Academy, and indicated to the writer the existence 

 of an unknown Plesiosauroid reptile. Subsequent correspondence with Dr. Turner resulted in his employing a 

 number of men, who engaged in excavations, and succeeded in obtaining a large part of the monster. Its vertebras 

 were found to be almost continuous, except a vacancy of some four feet in the interior dorsal region. They formed 

 a curved line, a considerable part of whose convexity was visible on the side of a bluff of clay shale rock, with seams 

 and crystals of gypsum. The bones were all coated with a thin layer of gypsum, and in some places their dense layer 

 had been destroyed by conversion into sulphate of lime. 



The scapular arch was found in large part adhering to the bodies and neural spines of a series of the anterior dor- 

 sal vertebras, and was detached from it at the Academy. The pelvic arch had been slightly crushed, and the lumbo- 

 sacral vertebras forced into contact with the ischia, where they remain. A broken extremity of the supposed ilium 

 was forced into the matrix which supports the ischia. Many of the dorsal and caudal vertebrae were sent, and remain 

 in continuous masses, so that the succession is readily traced, and the true relations of the extremities preserved. 



In removing the matrix from beneath' the vertebras, scales and teeth of some six species of Physoclyst and 

 Physostomous fishes were found, including an Enchodus and a Sphyraena, the latter indicating a new species, which 

 I have called S. carinata. These animals had doubtless been the food of the Elasmosaurus. 



