122 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.51. 



It seems to the writer that N. grcaciZiceps had the skull more de- 

 pressed at the anterior half of the frontals. As a result of this, as 

 Stock says, the nasals have their upper surface transversely convex 

 in front, but becoming flattened posteriorly. In N. texanum these 

 bones are rather more convex just in front of the hinder end than 

 in front. In N. texanum the end of the snout is apparently more 

 depressed than in N. graciUceps. The width is nearly the same in 

 the two skulls, but in the latter the height is 60 mm., while in N. 

 texanum it is only 48 mm. Unless a serious error is committed as 

 to the structure of the pterygoid bullae in N. texanum, these are 

 sufficient to differentiate the two species. In N. graeilheps the nasals 

 have a combined width of only U mm. ; in .V. texanum the width 

 is 57 mm. 



There are apparently differences in the two species as regards the 

 teeth. The type of N. graicili)ceps had not retained the teeth ; but the 

 size and forms of these may be determined from the sockets. Stock 

 had one tooth, apparently the second molar, which had been found 

 in the Rancho La Brea deposits. The sockets of the type skull and 

 the tooth mentioned show that the teeth of N. graciUceps were larger 

 than those of N. texanum. The anteroposterior diameter of the 

 second molar is 13 mm., and thus 2 mm. greater than in the same 

 tooth of N. texanum. In A'', gramlkeps the hinder face of the first 

 tooth was evidently convex from side to side; in N. texanum it is 

 slightly concave. 



