324 New Species of Aplodontia. 



series. Hence it is clear that Peters's animal was young, and 

 that the supposed difference was due solely to immaturity. 



The second point relates to the size of the post-zygomatic 

 notch, which Peters says is much larger in his specimen than in 

 that figured by Baird. Baird's plate shows very well the size 

 and form of the notch, as it exists in the seven skulls of A . rufa. 

 In the California animal this notch is still narrower, though 

 perhaps a trifle deeper; hence in this respect Peters's specimen 

 differs from both. 



The third point relates to the position of the mental foramen. 

 Peters says that it opens more anteriorly than shown in Baird's 

 figure. In all of the jaws of both species examined by me (16 

 in number) this foramen is situated more posteriorly than indi- 

 cated in the above mentioned plate. 



The fourth point relates to the position and angle of the open- 

 ing of the inframaxillarv canal — the inferior dental foramen. 

 Peters says that it is situated more posteriorly than indicated in 

 Baird's plate and that it is so placed as to be visible from above. 

 In the specimens examined its position agrees very well with that 

 indicated by Baird ; and whether or not the opening can be seen 

 from above depends neither upon age, sex, nor species, but solely 

 upon individual variation — as demonstrated in the series before 

 me. Two specimens of the same age, taken at the same place 

 and on the same date, present the extremes of this peculiarity. 

 In one the opening is distinctly visible from above ; in the other 

 it is entirely hidden by the ridge of bone which extends from the 

 condylar process to the posterior alveola. 



The fifth point relates to the breadth of the coronoid process 

 at the base. Peters states that it looks broader than in Baird's 

 figure. But since Peters himself did not feel sure upon this 

 point, and since the specimens at hand fail to show any tangible 

 difference in this particular, the character may be safely dis- 

 missed. 



Three other important points were mentioned incidentally by 

 Peters. The first relates to the size of the infraorbital foramen, 

 which in his specimen was "scarcely larger than in Tamias. 79 

 The smallest infraorbital foramen in the 16 skulls before me is 

 at least three times larger than its maximum condition in any of 

 the skulls of Tamias (upward of a hundred in number) in my 



