264 Uiiii'ersify of California Fuhlications in Zoology. [Vol. 7 



centers of molt inception, one at the anterior end of the animal, 

 the other in the mid-posterior region. From the anterior end, 

 the molt Qf course works backward, from the mid-posterior region 

 it works both backward and forward. 



The results of my study of the material at hand agree closely 

 with the characterization of the skull of the species as given by 

 C. Hart ^lerriam (1897b, p. 213). In our specimens the pre- 

 maxillae extend variously from 1.7 mm. in young specimens, to 

 3 mm. in two adults. The average length of these bones pos- 

 terior of a line joining the posterior ends of the nasals in four- 

 teen skulls at hand is 2.3 mm. The average of all the juvenals 

 taken separately is 2.04 mm., that of the adults 2.48 mm. The 

 jugals, while essentially parallel, converge slightly anteriorly, \ 



except in one specimen. I 



There is great variation in the size and shape of the inter- i 



parietal, as the table of measurements shows. In one old speci- 

 men (no. 7856) it has the form of a triangle pulled out anteriorly ' 

 and posteriorly as a result of the approach of the temporal , 

 ridges; in a ju venal (no. 7869), it is square. Although it is i 

 trapezoidal in form in most of the skulls examined its great : 

 variation in outline may be illustrated by the fact that in one it 

 is pentagonal, in another arrow-head shaped. In general it may 

 be said to be approximately square in the young specimens, 

 growing smaller and taking on a more triangular form with age, 

 due to the growth of the parietal bones. This reduction in size 

 is, according to C. H. Merriam (1895a, pp. 41, 62), due to two 

 causes, namely, the partial covering of it by the parietals, and its 

 resorption as a result of pressure along the suture between it and 

 the parietals. 



