1918] Stock: The Pleistocene Fauna of Hawver Cave 



487 



The differences in the dentition as noted above relate only to forms 

 in which the third lower tooth is just coming into function. They 

 become less evident as trituration progresses. 



MICEOTUS, sp. 



A fragmentary ramus without teeth is the only specimen of this 

 genus available. In the cave specimen, no. 21460, the mental foramen 

 approaches very closely the superior border of the mandible in its 

 position. This character is true also for Microtus montanus of the 

 Sierran region. No. 21460 differs from M. montanus and M. mordax 

 in that the lower border of the angle approaches more the level of 

 the inferior border of the horizontal ramus. It differs further from 

 these forms in that the posterior end of the angle is in a vertical line 

 with the posterior end of the condyle, in which respect it resembles 

 more the M. californicus group. 



On the external surface of the ramus the peripheral process over 

 the base of the incisor is broken, but it was evidently prominent and 

 apparently lies above the masseteric crest as in M. montanus. In 

 M. mordax the prominence lies in the crest while in M. californicus 

 the masseteric crest is continuous. The condyle is decidedly more 

 slender than in M. montan us and approaches that in M. mordax. The 

 internal dental foramen is situated very close to the inferior border 

 of the condyle, while in M. montanus, M. mordax and M. californicus 

 it lies well above the inferior margin. 



At the present time M. montanus ranges from Upper Sonoran to 

 Transition, while M. mordax is found in the Transition and Boreal 

 zones. Microtus californicus has the greatest zonal range. This 

 species ranges from the Lower Sonoran to the Canadian (Lower 

 Boreal) . 



The specimen from Hawver Cave may represent a form specifically 

 distinct from the groups living in the Sierran region today, but much 

 better fossil material must be awaited before this can be definitely 

 ascertained. 



LEPUS, probably n. sp. 



Very fragmentary material of the rabbit group is available. For- 

 tunately among these remains are several specimens of the third lower 

 premolar. According to Dr. L. R. Dice, 17 who has recently studied 

 the Tertiary lagomorphs of the Great Basin region, important taxo- 



1' Dice, L. E., Systematic position of several American Tertiary lagomorphs, 

 Univ. Calif. Publ., Bull. Dept. Geol., vol. 10, pp. 179-183, 1917. 



