244 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
acters closely conforming to the last named. Palatal shelf as in Myodes; 
zygomata much less laminar than in Myodes (nearly as in the larger Arvicole). 
Nasals and nasal branch of premaxillaries subequal; both very short, ending 
opposite anterior root of zygomata. Orbits less encroached upon by the 
cranial dome than in Myodes, but having a prominent pointed process 
for muscular attachments. Superior incisors as in A/yodes; and likewise as 
in that genus, roots of under incisors stopping opposite back under molars. 
Molar series long and strongly convergent anteriorly, as in Myodes, but the 
pattern of the crowns entirely different and strongly arvicoline, as follows:— 
Front upper molar of seven (five in Myodes) prisms: an anterior transverse 
spherical triangle, three internal lateral triangles, two external lateral trian- 
gles, and a (small, supplementary) postero-external loop. Middle upper molar 
of six prisms (four in Myodes): an anterior transverse loop, two external 
lateral triangles, two interior lateral triangles, and a (small, supplementary) 
postero-external loop. Back upper molar of six prisms: an anterior trans- 
verse loop, two external and two internal lateral triangles, and a posterior 
trefvil, or V or U. Front under molar of nine prisms (five in Myodes): an 
anterior trefoil, three external lateral triangles, four internal closed triangles, 
and a posterior transverse loop. Middle and back under molar each of five 
(or five and a half) prisms: an antero-external triangle (with a more or less 
evident anterior lobe abutting against the back loop of the antecedent tooth), 
two internal lateral triangles, one external lateral triangle, and a posterior 
transverse loop. All the lateral triangles of all the teeth alternating. External 
form stoutest and most compact in the subfamily; limbs the shortest; no 
external ears; muffle completely hairy except the very papillee; pelage dense 
and woolly; feet short, stout, both fore and hind completely furry both above 
and below, the longer hairs reaching usually far beyond the ends of the claws ;’ 
pollex obsolete, with abortive nail; third and fourth digits much longer than 
second and fifth, their claws periodically hypertrophied and quasi-duplicated 
by an enormous growth of corneous substance on their under surface; hind 
claws ordinary ; tail to end of vertebra shorter than the hind foot, but copi- 
ously comous, the terminal pencil usually longer than the vertebral moiety. 
Coloration subject to periodical changes: dark and variegated in summer, 
snow-white in winter. 
As will be seen by the above, the cranial characters and those of the 
incisive dentition are very nearly the same as in Myodes, but that the pattern 
