MOUNTAIN LEMMING MOUSE. Phenacomys orophilus Merriam

Field characters.—Body size about twice that of House Mouse; tail short, decidedly less than one-half head and body (fig. 20c); hind foot under 4/5 inch. Head and body about 4 inches (98-108 mm.), tail 1-1/8 to 1-1/2 inches (28-40 mm.), hind foot 3/4 inch (18-19 mm.), ear from crown about 3/5 inch (14-16.5 mm.); weight 3/4 to 1 ounce (21.0-30.2 grams). Coloration ashy, brown-tinged on back, whitish on under surface; feet and tail pale ashy.

Occurrence.—Sparse resident chiefly in Hudsonian Zone. Recorded at Ten Lakes (9200 feet altitude), Glen Aulin (7700 feet), head of Lyell Cañon (at 9750 feet) and near Vogelsang Lake (10,100 feet); single individuals taken in each place. Lives about patches of Sierran heather and under other plants characteristic of the same altitudes. Solitary.

Our first specimen of the Mountain Lemming Mouse was captured at an altitude of about 9750 feet in the head of Lyell Cañon on July 20, 1915. Mr. Charles L. Camp of our party had spent much time examining clumps of Sierran heather (Bryanthus breweri) for evidence of the rodent and had set several lines of traps in likely looking situations. This individual was taken in a trap set beside a log at a small hole out of which fresh earth had recently been pushed. On the top of a nearby rock and beneath some brush was a mouse nest with a hole at the side, and a trap set there had been sprung two nights previously. About 50 feet distant from the hole, and in a patch of heather, a pile of old droppings about 6 inches in diameter lay on the ground as if they had been deposited in a cavity beneath the previous winter's snow. The general situation was in an open stand of lodgepole pines at a level place dotted with clumps of heather. A rocky cliff stood to one side, and a stream ran by about a hundred yards distant.

At higher altitudes in Lyell Cañon, even up to 10,700 feet, masses of black and greenish droppings were found which, because of their similarity to the dung-masses of a species of Phenacomys in the coast region of California, were believed to be those of orophilus. Possibly the animals had wintered here beneath the shelter of down logs or rocks. Also in various situations, usually associated with the droppings, there were found numerous cuttings of heather and other plants, these cuttings being 1-1/2 to 3 inches in length. In one instance willow cuttings of the same nature were observed.

The four specimens of Mountain Lemming Mouse captured include 2 adult males, 1 female, and 1 male, sub-adult. In general appearance they remind one of meadow mice (see fig. 20c), to which they are certainly not distantly related. The short tail and pale gray coloration are the chief external features of difference. Obviously the population of this mouse is far below that of even the Cantankerous Meadow Mouse, else more would have stumbled into the many traps set in places similar to those in which our four specimens were taken.