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University of California Publications in Geology [Vol. 9 



Fig. 14. Aplo- 

 dontia?, n. sp. P 4 , 

 anterior and occlu- 

 sal views, no. 19798, 

 X 4. Cedar Moun- 

 tain beds, Stewart 

 Valley, Nevada. 



The character of the tooth resembles in general that of Aplodontia, 

 but differs in the shortness of the crown or in the depth of the enamel 

 lakes, as also in the number of enamel lakes. In minor details of 

 cross-section and in size, specimen 19798 would differ from any Aplo- 

 dontia species known to the writer. In the Recent aplodontias, and 

 in Aplodontia alexandrae of the Virgin Valley Middle Miocene, the 

 crown of P 4 is long hypsodont, and the bottoms of 

 the enamel valleys at the top of the crown disappear 

 in early wear. In specimen 19798, the enamel val- 

 leys reach the lower end of the crown. Either the 

 tooth was much shorter than in true Aplodontia 

 or the enamel valleys were deeper. 



On specimen 19798, there are four enamel lakes 

 shown on the occlusal surface. Two are on the 

 outer half of the surface, and two on the inner half. 

 In a Recent Aplodontia a fourth upper premolar 

 just about to come into use shows two external 

 valleys, which apparently correspond to the enamel 

 lakes seen in slightly worn teeth. A very shallow 

 valley runs transversely over the tooth from the 

 mesostyle to the inner border. In Aplodontia alexandrae an unworn 

 P 4 shows a form similar in general to that of the Recent species, with 

 the exception that the valley extending across the tooth from the 

 mesostyle to the inner border is divided into outer and inner depres- 

 sions separated by a wall. The outer of these two valleys is apparently 

 deep, the inner valley is relatively shallow. A somewhat worn speci- 

 men of Aplodontia alexandrae shows on P 4 three enamel lakes which 

 apparently correspond to the anteroexternal, posteroexternal and in- 

 ternal valleys. Three of the enamel lakes of specimen 19798 correspond 

 approximately to the three seen in P 4 of Aplodontia alexandrae. 

 The anterior and posterior lakes apparently correspond to the large 

 lakes in Recent Aplodontia. The anterointernal lake seems to cor- 

 respond to the anterointernal lake of worn teeth of A. alexandrae, or 

 to the large shallow valley in the unworn specimen. Two very small 

 canals in specimen 19798 may represent the middle outer valley next 

 the mesostyle in A. alexandrae, though this must remain doubtful. 

 The relation of the posterointernal lake of specimen 19798 to the 

 valleys of A. alexandrae is doubtful. This lake occupies the position 

 of a posterointernal valley in Meniscomys, which is presumed to be the 

 ancestor of Aplodontia. 



