28 BIOLOGICAL SOCIETY OF WASHINGTON. 



The parietal and supra-occipital bones co-ossify so early in life 

 that in the adults it is generally impossible to detect the suture 

 between them ; hence they are here measured together. They 

 are very much shorter in macrorhabdotes than in townsendL 

 measuring from 10.60 to 11.00 mm. (four-tenths of a millimetre 

 covering the limits of variation in nine specimens) ; while in 

 tovjnsendi two specimens measure respectively 13.50 and 13.00 

 mm. The average of the ratios of the length of the parietals and 

 supra-occipital, thus united, to the basilar length in eight skulls of 

 macrorhabdotes is 37.87 ; in two of townsendi it is 45-77- 



The first upper premolar is decidedly smaller in macrorhabd- 

 otes than in townsendi ; it has evidently ceased to be functional 

 and is fast becoming obsolete — one of many characters point- 

 ing to the higher differentiation of the new species. 



The pretty little Striped Squirrel which forms the subject of 

 the present paper is one of peculiar interest. It is surprising 

 that an animal of its size and diurnal habits, and one which 

 differs so markedly from even its nearest relative, should have 

 escaped so long the notice of the many naturalists and collectors 

 who have traversed the region. The most natural explanation is 

 that the Long-Eared Chipmunk is an exceedingly local species, 

 restricted in its range by certain physiographical conditions of 

 which we are at present ignorant — conditions which were influ- 

 ential, doubtless, in bringing about the modifications which dis- 

 tinguish it from its congeners and mark it as one of the most 

 highly specialized of the genus Tamias. That this genus is pe- 

 culiarly susceptible to environmental influences is amply attested 

 by the number and perplexing characteristics of the incipient 

 species already known from the United States. 



The specimens of this new species were collected by C. A. 

 Allen, of Nicasio, California, and the accompanying figure was 

 drawn bv Ernest E. T. Seton. 



