4:34 



University of California Publications. 



[Geology 



Description and Comparison. — P 4 of this specimen is made up 

 of two distinct but connected columns with two roots; while M a 

 is a prismatic column, slightly flattened anteroposterior^, and 

 with an indication of a fold on the inner side. The enamel of 

 the incisor comes well around to the outer side. The alveolus 

 of M 2 indicates that it must have been of about the same size as 

 M 15 but the broken end of M 3 shows a much smaller tooth. A 

 comparison with specimens of Perodipus shows that the two 

 have teeth of a fairly similar character, although in the Perodipus 

 generally P 4 does not show two distinct columns, especially in 

 worn teeth; M 3 is not so much smaller than M 2 ; the enamel of 

 the incisor does not come around to the outer side ; and the folds 

 of the molars vary, being sometimes lacking entirely, sometimes 

 indicated on the outside and in a few cases both on the inside and 

 outside. The jaw of D. parvus is smaller than in any specimen 

 of Perodipus and yet the tooth row is longer. In Perodipus the 

 angle of the ramus turns inward sharply, and back of M 3 the 

 dental foramen is set in a deep pit. D. parvus shows more 

 affinity with the genus Perognathus in jaw structure and even in 

 the pattern of the teeth, but its teeth are prismatic while those 

 of Perognathus ai*e short-rooted. 



Measurements. 



No. 125G6 



P 4 , anteroposterior diameter 1.4mm. 



M,, anteroposterior diameter 1.2 



P 4 . transverse diameter 1.3 



M lt transverse diameter 1.4 



Incisor, transverse diameter 0.7 



Incisor, anteroposterior diameter 1.0 



Length from anterior end of incisor to posterior end of tooth row.... 10.5 

 Height of jaw below P 4 3.2 



DIPRIONOMYS MAGNUS, n. sp. 

 Fig. 18. 



Type no. 12567, Univ. Calif. Col. Vert. Palae., a fragment of 

 a left ramus of the lower jaw with P 4 , M 1? M 2 , and a groove indi- 

 cating the size of the incisor. Cotype no. 12568, a portion of a 

 left ramus of the lower jaw with P 4 and a fragment of the incisor. 

 Locality no. 1103 at Thousand Creek, Humboldt County, Nevada. 



Specific Characters. — Larger incisor and deeper fold on inner 



