44 



University of California Publications. 



[Geology 



reaches down to the inferior margin of the jaw, which it may 

 follow for some distance. 



In the present state of onr knowledge there appear to he three 

 or four types represented in the Archaelurus-Nimravus group. 

 It is not certain that they represent distinct species and the niiin- 

 ber will possibly be reduced when more material is known. 



A. debilis is a small form representing the more primitive 

 extreme in premolar dentition and possibly in the form of the 

 canines. P.. has an anterior tubercle. The massaterie fossa is 

 relatively broad and the exostosis is large. The type skull is 180 

 mm. long, P 1 and P 2 are both present, the canine is not greatly 

 elongated. It represents a fully adult individual and possibly a 

 female. 



.4. debilis major. Large forms with variable premolar for- 

 mula, reduced exostosis, and wide massaterie fossa. Superior 

 canines moderately elongated, with serrated posterior edge, and 

 with basal anterior groove. Type skull No. 1681 (pi. 4), a 

 young individual; basal length 225 mm. Mandible No. 1679 

 (text-figure 16), referred to this species, is from a somewhat 

 larger individual with teeth but little worn. The inferior canine 

 has a serrated posterior margin, P„ is two-rooted, P :! with ante- 

 rior basal tubercle, and the exostosis is somewhat reduced. These 

 two young specimens exceed the old individual representing the 

 type of debilis by more than 45 mm. in skull length, which is 

 more than the ordinary range of sexual variation in cat skulls of 

 approximately this size. 



N. gomphodus has a generally reduced premolar dentition, 

 lacking both P 1 and P 2 . The canines are relatively long and 

 slender, though both characters are doubtless somewhat exagger- 

 ated in the type specimen. P., without distinct anterior basal 

 tubercle. Massaterie fossa relatively narrow. The skull charac- 

 ters separating this species from A. debilis are largely bridged 

 over by A. debilis major. 



N. eonfertus resembled N. gomphodus excepting in the char- 

 acter of the greatly shortened inferior diastema. Known only 

 from the lower jaw. 



The observations presented above indicate some of the diffi- 

 culties met in attempting to carry a separation of the generic 



