MAMMALS OF MINNESOTA. 177 
The lower jaw is elongated, with low coronoid and broad but 
not hamular angle. The skull is twice as long as wide. The 
length of the lower jaw is about three times its hight. 
The scapula differs from that bone in Arvicola by being less 
slender and having a short acromium and broad metacromium. 
The deltoid ridge of the humerus is fairly developed. The 
sternum consists of six sternebre, the manubrium being very 
broad anteriorly. The fibula is united with the tibia, as in - 
Arvicola, but is less slender, and the limb is proportionally 
longer. 
We have purposely omitted the dentition from the above 
account, preferring to quote Coues’ statements as the most sat- 
isfactory general account at hand: 
‘‘The molar series is both short and narrow, between one- 
sixth and one-seventh the length of theskull. . . . Themolars 
rapidly decrease in size from before backward, particularly in 
the upper jaw, where the last one is subcircular, and not more 
than half as large as the middle one, which itself is less than 
the frontone. . . . The molars of the upper jaw have three 
roots apiece, two external and one internal; those of the under 
jaw have buttwo, placed one after the other on the median line. 
The unworn molars of Hesperomys show a double 
lengthwise series of conical tubercles connected by lower cross- 
wise ridges, and the whole face of the tooth is encased in a 
sheet of enamel continuous with that of the sides of the tooth. 
The tubercles are not exactly opposite each other in 
crosswise pairs, but are half-alternating. Down between the 
bases of these conical eminences are seen furrows, the more 
readily noticeable because generally blackened, apparently by 
the sticking of foreign matter in them. They represent the 
deep, close-curved plications of enamel that penetrate the tooth 
from either side, the ends of the loops nearly or quite meet- 
ing in the substance of the tooth. . . . It will be seen that, 
after abrasion has commenced, the molar crowns will present a 
different pattern with eachstage of the process. . . . The 
student may imagine the top of a pigeon pie, full of humps and 
hollows, gradually razeed down by a succession of thin parallel 
horizontal slices. Letthe crust be the enamel,and the substance 
of the pie the dentine ; the first slice will shave off the tops of 
one or more humps, exposing the interior (dentine) in isolated 
places, these islands lying in a network of crust (enamel).”’ 
The habits seem to be as uniform as the structure, and our 
species may furnish an idea of the group. 
