AND AYES 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. Tf 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- 

 sostenuil elements are broader and more extended anteriorly. 



The American genera of Elasmosauridae may be compared as follows : 



Posterior cervical vertebrae without diapophyscs: ccrvicals longer, compressed, neck 

 very elongate. 



Elasmosaurus. 



Posterior cervical vertebrae with diapophyscs: ccrvicals quadrate, shorter, depressed, 

 rapidly diminishing in size, hence the neck shorter. 



ClMOLIASAURUS. 



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

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

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

 the same time, its remarkably inferior plcurapophyses. 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. oit. Proceed. Acad Nat. Soi., 1868, 1. c. 02. 

 Discosaurus earinatua, Cope. Leconte's Notes, 1. c. 



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

 usually complete skeleton in the Museum of tin; 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 distanoe north from the Smoky Hill Fork of the Platte river. Portions 

 of two vertebra presented by him to Or. Leconte when on his geological tour in the interest of the U. S. Pacific 

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

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



number of men, who engaged in exoavations, and succeeded in obtaining a large part of the monster. Its vertebra' 



were found to be almost continuous, except a vaoanoy of some four feel, 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 huge part adhering to the bodies and neural spines of a, series of the anterior dor- 

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

 sacral vertebra' to reed into contact with the ischia, where they remain. A broken extremity of the supposed ilium 

 was forced into l, he matrix which supports the ischia,. Many of the dorsal and caudal vertebra; 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 vertebra;, scales and tooth of some six species of Physoclyst and 

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

 I have called S. carinata. Those animals had doubtless boon the food of the Elasmosaurus. 



