20 PROCEEDINGS OF THE ACADEMY OF 



mens, and has nearly the same size. Tnterehevron ridges are entirely obsolete. 

 The articular extremities of the body are very like those of the Alabama 

 specimens, but the groove defining them from the acute margin is very incon- 

 spicuous or nearly obsolete. The deflections of the acute margin for the ac- 

 commodation of chevrons are comparatively and remarkably deep, especially 

 thoBe anteriorly. The spinal canal at the orifices is about seven lines wide ; 

 at the middle scarcely five lines. 



In all the specimens above indicated, a single venous foramen is situated on 

 the under side of the body, to the right of the median line. 



Comparative measurements of the specimens are as follow: 



Caudal from Kansas, Mississippi, Alabama, New Jersey. 



Length of body inferiorly 24 Z. 24 /. 23J 1 . 23 Z. 



Breadth ant. artic surface 36 36 33| 34 



Depth " " " 30 30 2Q\ 27 J 



Breadth post. " " 34 34 3l" 3l| 



Depth " " " 29 29 26 



Breadth costal artic. cavity 18 17 15 15 



Depth " " " 12 11 11 11 



Width between inf. margins of 



costal cavities 39 39 38 3S 



Distance fore and aft of chev- 

 ron surfaces 16 16 16 12$ 



We thus have the nearly corresponding caudal vertebra? of four individuals, 

 from the cretaceous formation of as many different localities, agreeing nearly 

 in size, proportions, form, and construction, but exhibiting decided peculiari- 

 ties in every case. Are these peculiarities to be considered of generic and 

 specific value ; of specific value alone ; or are they to be regarded as varia- 

 tions in the characters of a single species? From the specimens alone I 

 would incline to view them in the latter light, though I admit that each 

 variation may represent a different genus, or a different species of the same 

 genus. The reason for referring any one to a genus is equally good for all. 

 If the Alabama specimens be regarded as characteristic of Discosaurus, and 

 the Kansas one of Elasmosaurus, the caudal from Mississippi, with its nearly 

 flat ends, is quite as characteristic of a third genus, and the New Jersey caudal, 

 with its peculiarities, would form a fourth. The close correspondence in size 

 of the specimens rather favors the view that they all pertain to the same 

 species, though this maybe as coincidental as the discovery of the nearly cor- 

 responding vertebra in the four cases. The one which, in my view, is most 

 distinctive from the others, is the specimen from Mississippi, with the nearly 

 flat articular extremities of its body. It may be well to consider it as repre- 

 senting a species, and for this one I propose the name of Discosatirus planior. 



A vertebra, which accompanied the Discosauroid caudal from New Jersey, 

 from its appearance was supposed to belong to the same individual. It was 

 regarded as a posterior cervical, and is represented in figs. 1-3, pi. v, and 

 described on page 24 of the "Cretaceous Reptiles." It would appear by com- 

 parison rather to be an anterior caudal, and so far as I can judge in the im- 

 perfect condition of the specimens, resembles most nearly the fifth of the last 

 continuous series of twenty-two vertebrae of the Kansas skeleton. It appears 

 to agree nearly in form, constitution, and proportions with the corresponding 

 bone of the latter, but is rather smaller. 



Some years since I had the opportunity of inspecting some vertebral speci- 

 mens of a huge saurian in the possession of Mr. W. F. Roberts, who obtained 

 them from near Greenville, Clark Co., Arkansas. They are supposed to be of 

 cretaceous age, as the formation of that period is the prevailing one in the 

 locality in which they were found. Two of the best preserved of the speci- 

 mens, generally very imperfect, were briefly noticed in the Proceedings for 

 1854, page 72, and represented in figs. 1-3, pi. ii. The remains were observed 



[April, 



