80 



MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



under 2.00 ; most tails range between 2.00 and 2.50, and not a tail touches 

 3.00, which last is an ordinary length of tail for true leucopus. The feet give 

 no data (ranging from 0.65 to 0.77, with an average of about 0.77), neither do 

 1 be ears. The shorter tail, on an average, is the sole datum as far as form is 

 concerned. 



Close scrutiny of the table, however, shows that a considerable part of 

 the series has the tail equally or even exceeding the average of leucopus. 

 Secondly, this feature does not obtain in all the specimens from any given 

 locality; thus, No. 1932, with the shortest tail in the lot, is associated in 

 Kansas with veritable leucopus ; Nebraskan examples range from 1.75 to 2.75 

 in length of tail ; Utah ones from 1.80 to 2.30 ; Fort Crook ones about the 

 same; New Mexican and Sonoran ones from 1.93 to 2.65* In short, we find 

 in almost every locality a greater difference in the several tails than that dis- 

 tinguishing them collectively from leucopus; and we can only say that 

 they average half an inch less than the average of leucopus, about equaling 

 the trunk alone instead of about equaling the trunk plus three-quarters of the 

 head. 



As this finishes what we have to say of the form of these western 



United States mice, we here insert our table, and then take up some other 

 points. 



Table XIX. — Measurements of eighty-one (and list of other) specimens of supposed Hesperomys leucopus 

 sonouiensis Jrom the Middle Region, United Xtatts. 



* These seem to he leucopus. 



' Really from 1.93 to 3.05! For No. 145, collected by Mr. Clark on the Mexican Boundary, showed 

 a tail of S.05, and so had to be turned over to " texanns". 



