1917] 



Stock: Skull and Dentition of Nothrotherium 



161 



The fifth superior tooth, no. 8497, from Potter Creek Cave, re- 

 ferred to Nothrotherium by Sinclair, has been shown above to resemble 

 Megalonyx much more closely. It undoubtedly does not pertain to 

 the former genus. The characteristic features exhibited by this speci- 

 men cannot then be used as distinguishing Nothrotherium shastensc. 



It is evident from the above discussion that it is not possible to 

 separate N. texanum from N. shastcnse on the basis of characters at 

 present available. 



Dr. Hay considers the Texas form as very closely related to the 

 Rancho La Brea species of Nothrotherium, as indicated by a com- 

 parison with skull 15 contained in the collections of the Museum of 

 History, Science and Art of Los Angeles and described by the writer 

 in 1913. He remarks, however, that "One can not rely wholly on the 

 differences which are seen in the two skulls for additional specimens 

 may be intermediate. ' ' 4 " The characters exhibited by the teeth of 

 N. texanum fall easily within the range of variation of teeth in Rancho 

 La Brea skulls. One of the important skull characters cited by Hay as 

 distinctive of N. texanum is the structure of the pterygoid bulla. In 

 the Texas specimen the bulla of each side is open wide below, in which 

 respect it is in marked contrast to that of Rancho La Brea skulls. 

 In the latter the pterygoid bullae when undamaged are always com- 

 pletely closed below with the exception of an elongate orifice on the 

 inner ventral side. The pterygoid bulla in the skull of Nothrotherium 

 from Brazil, described by Reinhardt, lacks even this internal opening 

 and is apparently complete. 



Judging from the damaged condition of the skull of N. texanum 

 (the palate being severely injured and the pterygoid plates entirely 

 broken away in that specimen), such fragile structures as the ptery- 

 goid bullae can hardly be expected to remain entire. It is then reason- 

 able to snppose that the present appearance of these bullae in the Texas 

 specimen is to be attributed to injury sustained during preservation. 

 Dr. Hay is, however, of the opinion that the pterygoid bulla in A. 

 texanum remained widely open below during the life of the indi- 

 vidual. He states: "The bulla of N. texanum appears not to have 

 had a floor. The pterygoids seem to form a wall which surrounds the 

 cavity on both sides. On the median side the edge of the wall is 

 partly intact, partly injured. On the outer side the wall comes 

 down to a sharp thin edge which appears to be little if at all injured. 

 In places the edge is certainly wholly natural. Such being the case 



40 Hay, O. P., ibid., p. 121, 1916. 



