1914] Taylor: Aplodontia 299 



Coloration is remarkably uniform in the series of phaea, showing 

 only a very narrow range of individual variation. Of the four speci- 

 mens of nigra, three are young'. In coloration these differ only slightly 

 from the adult, and present the diagnostic characters of the species 

 as clearly. 



It should, perhaps, be emphasized that coloration serves unques- 

 tionably to differentiate A. nigra from any other species of the same 

 genus found in California. 



Cranial characters. — See table of measurements, following. Only 

 one specimen of Aplodontia nigra (no. 20320) is strictly comparable 

 with the series of four adult male specimens of Aplodontia phaea 

 listed in the table. The three other specimens show the open sutures 

 and immature characteristics of youth. 



Three characters stand out as specifically distinctive: the width of 

 the interpterygoid fossa, and the outline and breadth of the nasal 

 bones. .4. nigra (no. 20320) has the interpterygoid fossa thirty per- 

 cent broader than it is in the average of phaea, at least as shown in the 

 table of measurements. 



The outline of the nasals is different, A. nigra has this outline 

 dilated anteriorly, the broadest part of the nasals being about six 

 millimeters posterior to their anterior ends. In phaea the tendency 

 is for the broadest part of the nasals to be at the anterior points at 

 which nasals and premaxillae join. A. nigra, no. 20321, approxi- 

 mates the condition in phaea, while A. phaea, no. 20309. tends toward 

 the relation in nigra. The breadth of the nasals is definitely greater 

 in the Point Arena form than in phaea, however, the youngest speci- 

 men of the former exceeding in this respect all the adult males of the 

 latter measured. 



In other cranial characters A. nigra is nearly identical with A. 

 phaea, clearly exhibiting the comparatively close relationship of the 

 two coast forms. 



The Point Arena Aplodontia may be separated from any other 

 species represented in our collections on the basis of cranial as well 

 as external characters. Perhaps the most convenient is the length of 

 the incisive foramen, which is less in the crania of the two coast forms 

 than in comparable specimens of A. rufa, or in the species heretofore 

 described from California. Size also is a differentiative characteristic 

 when nigra is compared with rufa or with Californian species. 



It is perhaps worthy of note that the smallest, darkest forms of 

 Aplodontia are found along the western coast of the United States. 



