Williston.] Mosasaurs. 207 



Length of fifth cervical to rim of ball 49 mm. 



Transverse diameter of ball 35 



Expanse of diapophyses 90 



Length of fourteenth vertebra to rim of ball 54 



Transverse diameter of ball 40 



Vertical diameter of ball 33 



Length of eighteenth vertebra to rim of ball : . . . 50 



Transverse diameter of ball 40 



Vertical diameter of ball 36 



Length of thirtieth vertebra to rim of ball 54 



Transverse diameter of ball 46 



Length of quadrate 65 



Length of humerus 92 



Length of radius : 68 



Length of ulna 65 



Length of femur 95 



Length of tibia 70 



The specimen upon which this species is based was collected 

 by Chas. Sternberg, from near McAllaster, in the Fort Pierre. 



GENUS INCERTJE SEDIS. 

 Baptosaurus. 



Halisaurus Marsh, Amer. Journ. Sci., xliii, Nov. 1869 (preoc.) 

 Baptosaurus Marsh, Proc. Phil. Acad., xxm, Jan. 1870. 



This genus was based upon a New Jersey species, represented 

 "by a posterior cervical and an anterior dorsal vertebra ; the 

 right splenial bone with its concave articular face, and a small 

 portion of the base of the skull." Another species (H '. fraternus 

 Marsh) from the same region was established on an anterior 

 dorsal and two posterior dorsal vertebrae, found not far from 

 each other, and probably part of the same series." The charac- 

 ters given for the type species (H. platyspondylus Marsh) are 

 as follows: "This species is especially characterized by the 

 great depression of the centra of the vertebrae, which gives the 

 articular ball and cup a very transverse elliptical outline, ex- 

 ceeding in this respect apparently those of any other reptile. 

 The vertebrae, so far as known, are also elongate, and without 

 the zygosphenal and zygantral articulation." The coossifica- 

 tion of the cervical hypapophyses is also given as a distinctive 

 character. — 



