8 THE HISTORY OF THE PELYCOSAURIA, WITH 



anterior part of the centrum for the head, and a double one above for the bifid tubercle. 

 In the implantation of the teeth and their successional development these Reptiles 

 resemble the Mosasauria. These characters, with others mentioned below, indicate two 

 distinct families, which may be called Nothodontidce and Sphenacodontidce, from the 

 typical genera here described. 



" Nothodon lentus, gen. et sp. nov. 



" This genus of Reptiles may readily be distinguished by the dentition. In each 

 separate premaxillary there are two slender pointed teeth. In front of the maxillary 

 there are one or two similar teeth, followed by a number with narrow transverse crowns, 

 resembling in form the premolars of some carnivorous mammals. These crowns, when 

 unworn, have a central cusp, and on each side a tubercle, somewhat like that on the pre- 

 molars of the genus Canis. In the present species the first and last of the transverse teeth 

 are smaller than the middle ones. The limbs were short, the long bones had their 

 extremities covered with cartilage, but the carpals and tarsals were well ossified. The 

 centra were very deeply concave, and the tail was long. 



" The following measurements are taken from the type specimen of this species : 



MM. 



Length of maxillary bone 65" 



Space occupied by ten maxillary teeth 55 • 



Height of crown of second maxillary tooth 14- 



Height of crown of third maxillary tooth 9' 



Anteroposterior diameter 3' 



Transverse diameter 8 - 



Antero-posterior diameter of eighth tooth 5 ■ 



Transverse diameter 15 ■ 



" The present species was about five or six feet in length, and herbivorous in habit. 

 It was apparently slow in movement, and probably more or less aquatic. The remains at 

 present known are from New Mexico." 



This is one of Cope's Diadectidce. 



s 



" Sphenacodon ferox, gen. et sp. nov. 



" In the present genus the anterior teeth are somewhat like those of the reptile 

 described above, but the posterior, or more characteristic ones, are totally different. The 

 crowns are much compressed, and have very sharp cutting edges, without crenulations. 

 In the present species the carnivorous teeth are crowded together, and the crowns placed 

 slightly oblique, and twisted. The jaws were comparatively short and massive. The 



