WILLISTON : A NEW CRETACEOUS PLESIOSAUR. 243 



These known American plesiosaurs vary in length from that 

 of Doh ic h or •hi/n chops, described in the present paper, to that of 

 Megalneusaurus rex Knight, or of one whose remains are in the 

 University of Kansas museum, forty or more feet in length. 



The specimen of Dolichorhynchops osborni herewith figured was 

 collected in 1901 in the chalk of western Kansas by Mr. Charles 

 Sternberg. When received at the museum the skeleton was al- 

 most wholly contained in a large chalk slab, with all the bones 

 disassociated and entangled together closely. Owing to their 

 extreme softness, a characteristic of plesiosaur bones in gen- 

 eral, the labor of removing the different parts of the skeleton 

 and hardening them so that they could be handled has been 

 exceedingly slow and painful. The task of removing and 

 mounting the bones has required the skilled labor of Mr. Mar- 

 tin, the preparator, the larger part of a year, under my constant 

 supervision. The skeleton as now mounted is an example of 

 great skill on Mr. Martin's part and of much study. 



As mounted there is little conjecture. It is possible that 

 some of the vertebrae may be missing, but I do not think so, 

 unless a very few from the tail. Three or four vertebrae and a 

 few ribs were so badly decomposed that they have been modeled 

 in plaster, and a number of the dorsal spines could not be re- 

 covered. There is also doubt about the proper length of some 

 of the posterior ribs. The skull, after its complete removal 

 from the chalk, was found to be so very fragile that it was not 

 thought to be expedient to mount it with the skeleton. A 

 model, therefore, has been made, under my careful super- 

 vision, and mounted in its stead. The many bones of the limbs 

 were so intermingled that only a careful study permitted their 

 collocation, a task, aided, however, by a nearly complete pad- 

 dle of an allied form, about which there was less doubt. There 

 are nineteen vertebrae in the neck, thirty in the trunk, and 

 twenty-five preserved in the tail, which tapers very abruptly at 

 the extremity. There may have been a few more vertebrae in 

 the tail, though this is doubtful. The skeleton, as mounted, is 

 just ten feet in length. 



There are not a few new or strange characters presented by 

 this skeleton, especially in the skull, nearly all of the details of 

 which have been made out, such as the presence of two sepa- 

 rate and disconnected supraoccipital bones, peculiar frontal 



