400 



University of California Publications. 



[Geology 



C. H. Superior dental formula ? , °, -, 3 . P 3 a small, well- 

 developed cylindrical tooth as in Aplodontia rufa. P 4 with 

 strongly developed parastyle, mesostyle and metastyle, the latter 

 more distinct than in the Recent Aplodontia. The three upper 

 molars with well-developed styles. 



Median style absent in the lower molars and in P 4 . The 

 enamel of the inner wall in the inferior teeth extends back in an 

 unbroken surface to a prominent style on the posterior side of 

 the inner wall. 



The unworn P 4 of A. alexandrae differs from that of A. rufa 

 in the presence of a longitudinal median ridge separating the 

 median part of the tooth transversely into two lakes. In A. rufa 

 the median lake extends from the ectoloph to the inner wall of 

 the tooth. 



SUPERIOR DENTITION. 



The upper teeth are well represented in no. 11325 (fig. -1) ; 

 no. 11898 (fig. 6) ; and in no. 11899 (figs. 5a, 5b, 5c), an unworn 

 premolar four. These specimens show different stages of wear. 

 In no. 11325, P 4 , a worn tooth, shows the protocone, metacone, 

 and paracone to occupy approximately the same position as in a 

 specimen of Aplodontia, figured by Matthew and Gidley. 4 The 

 molar teeth closely resemble those of Aplodontia. 



In no. 11898 (fig. 6) the tooth series lacks left M 3 and right 

 P 3 . The teeth are more worn than in no. 11325 with a pattern 

 much as in Aplodontia rufa. The small P 3 is excellently pre- 

 served in the left maxillary. P 3 of the right is broken at the 

 alveolus, showing the root of the tooth in place. The frontals 

 are completely broken away with the superior ends of the tooth 

 series exposed. The roots are fully open and show the typically 

 hypsodont character. The mesostyle extends to the tip of the 

 root as seen in Recent specimens of Aplodontia and in the 

 Quaternary forms from Potter Creek Cave. 



In no. 11899 (figs. 5a, 5b, 5c), an unworn fourth premolar, 

 there are four deep lakes, an anterior, a median, a posterior, and 



* Op. eit. 



