102 
9. Microtus pennsylvanicus drummondii (Audubon and Bachman) 
Drummond Meadow-mouse 
This species caught at camp and in almost same sort of habitat as red- 
backed voles. Two traps set at a hummock showing mouse runways in 
muskeg, sometimes caught a mouse of each species. All present species 
taken at low level. One specimen caught in a trap baited with fresh 
meat; but these mice, like those of three other species, baited most success- 
fully with a mixture of burned bacon grease and strong cheese. Oatmeal 
useless. 
Specimens: Four. 
May 31, No. 5628, 9 juv., 126-35-16, Hubrick’s camp, Chitina river. 
June 6, No. 5633, & juv., 130-37-17, 
June 15, No. 5642, $, juv., 130-35-16, “ “ 
July 22, No. 5655, <? juv., 131-35-18, 
These specimens all juveniles and not quite suitable for comparing measurements; 
being smaller than average, and averaging more grey in colour than typical drummondii. 
Skulls of all four specimens check up same in teeth characters — first upper molar with a 
normal truncate posterior triangle; second upper molar with four closed triangles and a 
rounded posterior loop, latter being small; third upper molar with three closed triangles. 
Second upper molar characteristic for whole pennsylvanicus-group which here reaches near 
northwestern limit of range of this very widely distributed species. 
10. Microtus yakutatensis Merriam Yakutat Tundra Vole 
Timber-line mice not numerous and their work observed only here and 
there in clumps of last straggling willow. Their runways, midden-heaps, 
and fresh cuttings evidences of occupation in a few of upper hollows in 
higher slopes investigated. Four of these voles, taken August 7, agreed 
with a single male caught in same locality July 18. A female, August 7, 
carried five large embryos. Timber-line mice were invariably fly-blown. 
As traps always attended in morning before flies abroad, state of mice 
indicated that they had been active and got caught during the previous 
day. 
Specimens, five, of this large form of operarius - group (tundra voles) of meadow mice, 
taken at Chitina River glacier, at about 4,500 feet elevation. 
July 28, No. 5651, c? 168-47-20 
August 7, No. 5658, $ 168-46-19 
No. 5659, & 162-45 
No. 5660, <? 171-45-20 
No. 5661, 9 152-40-19 
Skull: Basal length, 26-5 mm. Nasals, 7-8. Zygomatic breadth, 18. Mastoid 
breadth, 11*5. Alveolar length of upper molar, 7. Skull rather long and slender, angular, 
and well-ridged. Nasals slender, ending even with arm of premaxillse, with medium con- 
striction. Incisive foraminia short, constricted posteriorly. Incisors projecting well in 
front of nasals, but not excessively so. Colour dusky grey, belly with decidedly buffy 
tinge. Distinctive characters of operamts-group well marked in all specimens, namely 
second upper molar with four closed sections and no posterior loop; first lower molar with 
four closed triangles and rounded anterior loop; molars moderately heavy; audital bullse 
medium. Dentition of all specimens similar, except that in two specimens first lower 
molar shows appearances of five closed triangles instead of four triangles and a rounded 
anterior loop. All microtine series, however, show considerable variability in both pat- 
terns. 
Strong probability that Microtus yakutatensis intergrades with Microtus operarius 
operarius (Nelson), Alaska tundra vole, of western and northern Alaska coast regions, or 
with Microtus operarius endoecus Osgood, Yukon tundra vole, of central Alaska and 
Yukon, but in absence of specimens from intermediate districts, stands as a distinct 
species. 
