398 



University of California Publications. 



[Geology 



During the past summer a continuation of the work begun in 

 1906 was carried on by a party from the University of Cali- 

 fornia, organized and supported financially by Miss Annie M. 

 Alexander. The field party spent the greater portion of the 

 summer in Virgin Valley and the adjoining regions, and obtained 

 a considerable collection of material representing the fauna of 

 these beds. Among the mammalian specimens obtained, one of 

 the most interesting series represents the peculiar group of 

 aplodont rodents, which has previously been known fossil only 

 by the specimens obtained in the Quaternary fauna of Potter 

 Creek Cave and Hawver Cave. This group, represented by the 

 living Aplodontia, has occupied an isolated position among the 

 Rodentia and comparatively little has been known of its affinities. 

 Valuable suggestions as to its relationships have been made by 

 various authors, particularly in recent papers by Sinclair, 2 and 

 by Matthew and Gidley. 3 As is shown in the following article, 

 forms very closely allied to the modern genus Aplodontia occur 

 in the Virgin Valley region in association with a fauna contain- 

 ing such forms as Mylagulus, Dipoides, Hypohippus, Mery chip- 

 pus, Palaeomi rij.r, and Chalicotherium, with various other types 

 which represent a late Tertiary fauna. 



DIAGNOSTIC CHAEACTEES. 

 Aplodontia Alexandras, n. sp. 



Type specimen, no. 11325, Univ. Calif. Col. Vert. Palae. 

 Maxillaries with slightly worn teeth. Cotypes, no. 11898, Univ. 

 Calif. Col. Vert. Palae. Maxillaries with nearly complete den- 

 tition; no. 11899, left P 4 , unworn tooth; no. 11897, right ramus 

 of mandible with complete dentition with exception of incisor; 

 no. 11909, right ramus of mandible with complete dentition. 

 Locality, late Tertiary beds, Virgin Valley and Thousand Creek, 

 Northwestern Nevada. 



Larger than Meniscomys hippodus Cope, Middle John Day, 

 Oregon. Smaller than the Recent Aplodontia rufa Merriam 



2 Am. .lour. Sc., vol. 15, p. 143. 1903. 



3 Anier. Mus. Nat. Hist., vol. 20, p. 206. 1904. 



