THE SKITLL OF BRACHAUCHENIUS, WITH OBSERVA- 

 TIONS ON THE RELATIONSHIPS OF THE PLESIOSAURS. 



By Samuel W. Williston, 



Of the University of Chicago, Chicago, Illinois. 



The type of the genus and species Brachauchenius lucasi Wilhston "- 

 is an excellent specimen in the collection of the United States 

 National Museum from the Benton Cretaceous of Western Kansas. 

 The genus is of unusual interest because of several remarkable 

 characters previously unknown among the plesiosaurs, which it 

 possesses, in particular the union of the palatine bones in the middle 

 line, and the very short neck. A second specimen belonging to 

 the same genus, from the Eagle Ford Limestone of Texas, also 

 forming a part of the collections of the United States National 

 Museum, was kindly submitted to me for study by the authorities 

 of that museum, a brief notice concerning which was published 

 in Science for June 19, 1903. 



These two specimens supplement each other, the type specimen 

 showing the underside of the skull and the connected vertebral 

 column as far as the lumbar region (Plate XXXIV), while the 

 present specimen permits a thorough examination of the upper part of 

 the skull, and has, also, eighteen of the early vertebrae, and a part 

 of the front paddle. The most careful comparisons fail to discover 

 generic differences between the two specimens, nor can I detect 

 specific differences even. The Texas specimen is partly inclosed 

 in a hard limestone matrix, and it is possible that, when the under- 

 side of the skull shall have been cleaned up, specific differences 

 may be apparent, but I do not think so. The specimen is slightly 

 smaller than the type. The Eagle Ford Limestone is known to be an 

 equivalent of the Benton Cretaceous, and I suspect that the imme- 

 diate horizon in which the specimen occurred will prove to be an 

 exact equivalent of that which ^aelded the Kansas specimen. 



^— . . — _ — • — 



a Field Col. Mus., Pub. No. 73, Geol. Ser., II, p. 57; Lucas, Smithson. Misc. Col. 

 Quart., I, p. 96. 



Proceedings U. S. National Museum, Vol. XXXII— No. 1540. 



