482 University of Califorma Publications in Zoology [ Vou. 17 
The ratio of the width of the angular portion of the jaw to the 
length of the jaw undergoes, in specimens measured, a 5 per cent 
increase with age. In youth there is a smooth space between the inner 
prominence of the angle and the ridge in front of the masseteric fossa, 
while in old age there is a tendency for this ridge to be continued 
Figs. N-P. Dorsal view of crania of young specimens of Aplodontia rufa 
phaea, to illustrate marking off of interparietal elements. X 1. Fig. N, no. 
20302, Mus. Vert. Zool.; fig. O, no. 20308, Mus. Vert. Zool.; fig. P, no. 20316, 
Mus. Vert. Zool. 
