MURiDAI—SIGMODONTES—H. LEUCOPUS SONORIENSIS. 85 
. 
TABLE XX.—Measurements of sixty-nine (and list of other) additional specimens of British American and Arctie 
HESPEROMYS LEUCOPUS, mostly of the “ sonoriensis” style—Continued. 
5 = 
NORE EO== Tail to end 
of— 
: re) < 
S Locality. * Collector. ‘= : 3 & Remarks. 
EI Sulla Pssl eh este Ge Mitek ee 
Az) A co 5 Cc) o 3 5 3 a 
A 8 8 ° ia > is q g 
4160, >| Kort Simpson@-=- =| dose ROSS ees | ean =||lpeeees tee ame Se eO! | er GON eG OO! re morose siniesetell teens Alcoholic. 
TOU os ee 3200s. Senos ctoaeis ar] wees Ol sammie fates: |eaatesel| com amis eectanaligaactay aera! sonnel mee es ORI (3 Wee beech’ Co 
LOW. Sos dO mia canccee esa cad| tee GOnas scr aed |paciace eats Teens |enconl cooueltoces lmemese 0.77 “omeliloe 
LONG; ||-e2¢doj-2-o--ycecnvaes| s752d0l tere se-| eee ce|soee | oenoee len san eo sen|ieceeelt meses (0:80) | 22 = Skins in alcohol | 
OU cee eetecenesees-4 sth) cosepeanicy beccod bce Bester Feseenl betes | coen Banas HOxaG) |e ==: eatih 
| 10115 Boece Ser eer laeeee | esate 0578) |peae ..-.do. 
TOL 
to smolts ces cannon foes O lees onairio=nl|| some esac lisscas|-sees es |) caneaihie aoe Ee cat Rotoee ls epee pee edOs 
7563) 
Nore —We have brought together our entire Arctic series of H. leucopus under the head of “ sonoriensis”’, and nearly 
all our specimens will be found labeled ‘‘H. leucopus var.’ It is hardly necessary to add t however, in this series every 
grade of approach to ordinary United States lewcopus is found, and that a certain percentage of the specimens are identical 
with Massachusetts skins, for example. 
Turning now to the matter of color, we find that certain differences in 
this respect have been ascribed to sonoriensis as diagnostic. This we can 
” inter se that it 
prove, first, to be so variable with specimens of ‘sonoriensis’ 
cannot distinguish them inter alia; and, secondly to be dependent upon local 
chmatic influences. It fluctuates between wide extremes, and is assuredly 
unreliable, both on this account and because it is within the ordinary limits 
of color-variation of leucopus (see under ‘ 
‘gambeli” and ‘‘austerus”). The 
intensity of coloration has precisely the same relation to hygrometric influ- 
ences that Mr. Allen pointed out in the case of birds: the depth of color is 
in direct ratio to the mean annual rain-fall, or, in other words, to average 
humidity of the atmosphere. In dry, treeless regions, we have the palest 
forms; while. the darker-tinted specimens occur in moist, wooded localities. 
gambeli” and ‘ austerus”, 
This is precisely correspondent to the case of ‘ 
already noted. Some of our palest prairie specimens almost suggest albinism ;— 
most of the Nebraska series are remarkably pale, with an indistinct or almost 
inappreciable darker dorsal wash. Fort Crook specimens are darker than the 
average (just as the Fort Crook Arvicolas are), approaching austerus in this 
respect; Utah and New Mexican samples are intermediate. The narrowness 
of the dark stripe along the upper surface of the tail is simply of a part with 
the general pallor; so is the hoariness of the ears, which appears as a sort of 
silvery edging in most specimens. (Cf. per contra Bairn, op. cit. 474.) 
Recurring now to the Arctic series, we find that instead of being paler 
than average leucopus, they are almost without exception darker. In this 
