51 
At Aitken lakes, northwest of cape Dorset, a large number of curiously 
shaped burrows in sandy ground were noted in mid-July, 1926. The 
burrows were of a size such as the back lemming would make and scarcely 
could have been made by any other mammal. Their unusual feature was 
the mounds of sand built up at the entrances and exactly like those made 
by ground squirrels. The sand in some of the mounds amounted to a 
quart or more. Excreta and tracks in the sand indicate that the burrows 
belonged to trimucronatus. Similar burrows had not been seen previously 
anywhere on Baffin island, but on August 7, 1926, were seen again at the 
head of Amadjuak bay on low, dry, mossy ridges. The material excavated 
was largely brownish loam. One mound consisted of fine sand with many 
fine particles of graphite. Lemmings, at this time, were quite common 
at Amadjuak bay. 
Allen and Copeland (1924, pp. 8-9) record that the MacMillan expe- 
dition secured several specimens of trimucronatus at Bowdoin harbour and 
the west coast north to latitude65 degrees. Corporal F. Mclnnes, R.C.M.P., 
informs the writer, under date of March, 1927, that during the previous 
year, lemmings were very numerous at Ponds inlet. In all probability 
they were trimucronatus. 
Kumlien did not find trimucronatus in Cumberland sound in 1877-78. 
At that time it may have been passing through one of its periods of great 
scarcity, as seems also to have been the case with Dicrostonyx groenlandicus , 
of which Kumlien secured only one specimen on Baffin island. Hantzsch 
(1913) makes no mention of trimucronatus , but does list D. groenlandicus 
which, according to the writer’s experience, is decidedly scarcer on Baffin 
island. Perhaps the periods of abundance of the two species alternate. 
Trimucronatus forms colonies in abandoned Eskimo campsites and in 
low, rock ground along streams; dispersed it occurs over the tundra, on 
low ridges, and up mountain slopes. On Ptarmigan mountain, Pangnir- 
tung fiord, on December 18, 1925, tunnels and feeding grounds were seen 
at an altitude of 1,500 feet and up to heights of 1,000 feet the species 
appeared as prosperous as at lower levels, but above 1,000 feet the numbers 
gradually diminished. On a mountain north of Koukdjitariak river, 
Pangnirtung fiord, on December 20, 1925, a few, fresh, lemming burrows 
in the snow and runways on the surface were observed at a height of 2,500 
feet as determined by an aneroid. 
The back lemming usually travels at a walk, the footprints then being 
a trifle over 2 inches apart. Occasionally the animal bounds along and 
the footprints are in couplets 3§ inches apart with the right and left 
imprints separated by an inch, the trail closely resembling that made by 
the least weasel, except that the left and right footprints are not offset 
with respect to one another. The footprints in snow are considerably 
larger than would be expected, a peculiarity exhibited in the case of all 
animals, particularly after sunny weather, for the effects of the sun rays 
are accentuated in the hollows which in these cases are footprints. The 
lemming throughout the winter tunnels upward through the snow even 
when of considerable depth, and in a limited degree travels on the surface 
despite the cold. Like Microtus, they are very active under the snow, 
where they have a network of trails through the vegetation, with here and 
there globular grass nets, all of which is revealed when the snow leaves in 
June. 
