130 



CALIFORNIA ACADEMY OF SCIENCES 



[Proc. 4th Ser. 



mcdiiis at hand (Nos. 174431, 174425, and 174432, U. S. Nat. 

 Mus.) show ratios of 28.6, 34.3, and 29.3 per cent respec- 

 tively; while two skins of orophilus (Nos. 109103 and 109102, 

 Biol. Surv. Coll.) show ratios of 30.5 and 28.1 respectively. 

 Of thirty-six specimens, representing eleven different species 

 of the subgenus Phenacomys, the measurements of which are 

 recorded in the literature, in only two does the ratio exceed 

 26.0 per cent, and in the majority it falls below 25.0. More 



than that, the average ratio of thirty-one additional specimens, 

 representative of the subgenus Phenacomys, falls below 26.0 

 per cent. These specimens constitute all of which measure- 

 ments have been found by the writer in the literature. 



Miller (1896, p. 24) asserts that length of tail in the 

 Microtiiicc, being more unstable than certain other characters 

 because more readily modified to fit a species to special require- 

 ments of its environment, is less important than these other 

 characters in the diagnosis of subgenera. It would seem to 

 the writer, however, that such a marked difference as seems 

 to hold in this respect between the alhipes-longicaudus group 

 on the one side and the other species of Phenacomys on the 

 other should be regarded as of at least subgeneric value. 



