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GEO R Y C H U S TRIMUCRONATU S.-Rich. 
Back’s Lemming. 
PLATE CXX.— Figs. 2 and 3. 
G. Auriculis vellere Lrcvioribus, naso obtuso nigro, palmis tetradactylis, 
unguibus lanceolatis cur vis. ungue pollicari lingulato, tricuspidato, corpore 
supra saturate castaneo, latere ferrugineo, subtus cinereo. 
CHARACTERS. 
Ears, somewhat shorter than the fur ; nose, blunt and black ; four claws on 
the fore feet of a lanceolate form, and a somewhat square thumb nail with three 
small points at the end ; body, dark chesnut above, reddish-orange or rust colour 
on the sides, gray beneath. 
SYNONYMES. 
Arvicola Trimucronatus. Rich, Parry’s Second Voyage, Append., p. 309. 
“ (Geortchcs) Trimucronatus. Rich., Fauna Boreali Americana, p. 130. 
DESCRIPTION. 
In size a little inferior to the Hudson’s Bay Lemming, or nearly equal 
to the Norwegian species ; head, flat and covered by moderately long fur ; 
ears, shorter than the fur, inclined backwards, and but thinly clothed with 
hair ; eyes, small. Upper lip, deeply cleft ; nose, obtuse, with a small 
naked but not pointed or projecting tip ; whiskers, numerous ; inside of the 
mouth, hairy, the hairs arising from projecting glandular folds ; upper inci- 
sors, presenting a conspicuous but shallow groove with an obliquely 
notched cutting edge ; there are three molar teeth on a side in each jaw. 
Fore legs, short ; feet, moderately large, and turned outwards like those of 
a turnspit. 
The tail projects a few lines beyond the fur, and is clothed with stiff 
hairs converging to a point ; there are four toes on the fore feet, armed 
with moderate sized strong nails curved downwards and inclining out- 
wards ; they are of an oblong form, convex above, not compressed, exca- 
vated underneath more broadly than the nails of any of the other American 
Lemmings, and have sharp edges fitted for scraping away the earth ; the 
thumb is almost entirely composed of a strong nail which has two slightly 
