Vol. 5] Furlong. — An Aplodont Rodent from Nevada. 401 



an inner. The metaconule and protoconule unite to form a high 

 longitudinal ridge, the anterior end of which joins with the proto- 

 cone to form the boundary walls of the inner lake. The eetoloph 

 is produced externally in a prominent mesostyle. The metacone 

 and paracone give rise to transverse ridges that join the meta- 

 conule and paraconule respectively on the median ridge. The 

 paracone ridge separates the anterior lake from the median lake 

 and the metacone ridge separates the posterior lake from the 

 median one. 



A left fourth premolar of no. 11325 (tig. 4) shows advanced 

 wear. The large lakes in no. 11899 are represented in no. 11325 

 by small lakes, two placed anteriorly and one posteriorly on the 

 crown. The fourth premolar in no. 11898 (fig. 6) show r s further 

 wear, the cuspules are completely worn away and the worn crown 

 closely resembles that in the Recent Aplodontia. 



INFERIOR DENTITION. 



Inferior dental formula 1 , „, 1} ... In Aplodontia rufa (no. 

 3748, Univ. Calif. Mus. Vert. Zool.) the inner side of the teeth 

 a little anterior to the middle portion is produced into a promi- 

 nent style that is constant throughout the depth of the teeth. 

 This character is also present in Aplodontia from Totter Creek 

 Cave. 



In a mandible of Meniscomys hippodus (no. 606, Univ. Calif. 

 Col. Vert. Palae.) and other specimens in the University collec- 

 tion the teeth have prominent median styles. The teeth of 

 Meniscomys also show a decided tendency to hypsodonty. The 

 style is confined to the upper portion of the teeth, not extending 

 below the alveolar border. 



In Aplodontia alexandrae uos. 11897 (tigs. 1 and 2). 11909 

 (fig. 3), and others, the inner walls of the teeth are produced 

 posteriorly in a gently concave unbroken surface to a prominent 

 style on the posterior region of the inner margin of the teeth. 



