1912] 



Kellogg: Pleistocene Rodents of California 



161 



8 10 



Fig. 7. Thomomys microdon. Anterior portion of skull, left side, no. 

 5738. 



Pig. 8. Thomomys leucodon. Anterior portion of skull, inferior view, 

 no. 4649. 



Pig. 9. Thomomys leucodon. Anterior portion of skull, left side, no. 

 5622. 



Fig. 10. Thomomys leucodon. Anterior portion of skull, inferior view, no. 

 5622. 



Figs. 7 to 10 natural size 



The writer has referred a number of lower mandibles — about a 

 dozen from each cave — to this form on account of their small 

 size, and one portion of a skull from Potter Creek Cave which 

 corresponds closely to the type specimen. In Samwel Cave the 

 specimens were found at depths varying from near the surface 

 to thirty-six inches, in Potter Creek Cave from four inches to 

 one hundred and sixty. 



THOMOMYS LEUCODON Merriam, C. HJ 



There are six specimens, one an anterior portion of a skull 

 without teeth, no. 4649, from Samwel Cave, another anterior 

 portion of a skull with incisors, P 4 , M 1 , and M 2 , no. 5622, and 

 four lower mandibles from Potter Creek Cave, which, on account 

 of their size and shape, have been placed under the leucodon 

 group of Thomomys. There are certain characters shown by 

 these specimens, especially the fragments of skulls, in which they 

 differ from specimens of T. leucodon navus from the collection 

 of the California Museum of Vertebrate Zoology. No typical 

 specimens of T. leucodon were available, but the skulls of the 

 subspecies navus do not differ from those of the typical form in 

 the points mentioned. 



In the fossil specimen, no. 4649, from Samwel Cave the in- 



