MURID^J— SIGMODONTES— H. LEUOOPOS SONORIENSIS. 



83 



We will next show that the short-tailedness ot var. sonoriensis likewise 

 characterizes, almost unexceptionally, the mice of Arctic North America. 

 Indeed, this fact has already been shown in the previous table, which we intro- 

 duced to settle the myoides question ; these additional specimens, indeed, 

 are merely the rest of our Arctic lot, positively the same as those of the 

 "myoides" table. Most of these Arctic ones are noticeably larger than United 

 Stares specimens, as was to have been expected ; they average about 3.66 in 

 length, with tail about 2.75; while the relative lengths of tail and body of 

 sonoriensis are nearly repeated, about half an inch has been added to the abso- 

 lute lengths of both trunk and tail. The feet are rather smaller, both abso- 

 lutely and relatively, than in true leucopus, averaging only 0.75, notwithstanding 

 the increase of general size. This feature, as well as the shortness of the tail, 

 might be explained upon the well-known law of smallness of peripheral parts 

 in Arctic animals ; but it is curious that it should correspond exactly with the 

 shortness of tail of the New Mexican animals, which, of course, are not 

 amenable to this law. ' The tail and feet are both unusually hairy. Here is 

 the table: — 



Table XX.— Measurements) of sixty-nine {and list of other) additional sjiecimeus of British American and Arctic 

 HK8PEUOMYS leucopus, mostly of the "sonoriensis" style. 



[Not muck reliance can be placed on the dry measurements, as the skins are all badly prepared, being almost without 

 exception overstuffed, the tails being skinned and distorted, and the feet having the toes curled up.] 



