158 University of California Publications in Geology ["Vol. 7 



masseteric fossa is usually continued across the lower side of the 

 ramus to the inner prominence of the angle, and that the wall 

 in front of the fossa above the angle, on the inner side of the 

 ramus, is vertical for a relatively long distance below the open- 

 ing of the alveolar canal. A large number of mandibular rami 

 and a few fragments of skulls showing the upper tooth rows and 

 palate are found in both caves, and a careful study of these, 

 together with live skulls of Aplodontia major from the collection 

 of the California Museum of Vertebrate Zoology taken in the 

 Shasta region, shows that not only is the shape of the dental 

 foramen not constant, but that the other two characters given 

 vary according to the age of the individual, the continuation of 

 the ridge across the ramus and an excessive vertical height gener- 

 ally indicating age. In taking measurements of the upper and 

 lower tooth rows in the fossil specimens, a range of variation was 

 found, from a Samwel Cave specimen with a lower tooth row of 

 16.7 mm., up to one from Potter Creek Cave measuring 20.5 mm. 

 The conclusion is that these specimens represent individuals of 

 all ages from very young to very old. On the whole, the lower 

 tooth row of the fossil specimens averages slightly longer than 

 in the living species, the average length of twenty-five specimens 

 from Potter Creek Cave being 18.6 mm. j so that this factor, 

 taken in conjunction with the fact that the ridge across the 

 rami of the fossil specimen is, on the whole, slightly more pro- 

 nounced than in all but one of the five specimens of A. major, 

 would support the view that the fossil form is a distinct sub- 

 species. 



PEROMYSCUS MANICULATUS GAMBELI (Baird) 



A portion of the skull with left upper tooth row from Samwel 

 Cave has been referred to this widely distributed species of the 

 genus, as it presents no characters which might distinguish it 

 specifically. 



NEOTOMA CINEREA OCCIDENTALIS Baird 



Of all the rodents the most abundant remains from both caves 

 are those of Neotoma. They occur at varying depths in abund- 

 ance, but unfortunately consist chiefly of lower mandibles. A 

 new species, Teonoma spelaea, has been described from Potter 



