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 /ewcopus. The feet give 
no data (ranging from 0.65 to 0.77, with an average of about 0.77), neither do 
the ears. The shorter tail, ov 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 /eucopus ; 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 Jdewcopus; and we can only say that 
they average half an inch less than the average of /eucopus, 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 
SONORIENSIS from the Middle Region, United States. 
[N. B.—Many of these specimens are not fairly distinguishable from ordinary leucopus. } 
Nose to— ee 
3 Locality. Collector. 3 : E E Remarks. 
A AlA/O/a|/F/AR|/s/e/a 
9838 | Fort Ellis, Mont ........-... ¥. V. Hayden ..-....- Seal secre Peae 3. 75/2, D0}... .].... 0. 75).--- Dry. 
4309 | Near Platte River ....:.....].----- iy penenem eee anea| [Sse ----/4. 00/2, 40)....].... 0.78|..-.| Dry; stretched. 
- 4310 ae= |e a=. (0178) oa) Dry. 
4311 on | PES be Rese bose 
1398 5 ee ee Ohta] 2-4 | Dry 
1399 Bee es ETC one Saas dO. 
1969 ...|0. 33/0, 73)....| Alcoholic. 
651 .---|----|0. 80]... | Dry 
702 --|0.77| --.|----do.* 
703 == (0.74) -—.\||. 22.00." 
1779 --|0. 76)....| Dry. 
1780 --.|..-.].-..] Dry; young. 
1781 Re lh elke eedos 
1782 -.|0. 80] .-..] Dry. 
1783 Bel bord Beas) bookies, 
* These seem to be leucopus. 
* Really from 1.93 to 3.05! For No. 145, collected by Mr. Clark on the Mexican Boundary, showed 
a tail of 3.05, and so had to be turned over to ‘‘texanus”’. 
