A a 
ZAPODID—ZAPUS HUDSONIUS—EXTERNAL CHARACTERS. 473 
greatly exceeds that of the body; a peculiar condition of the external ear; 
and a physiognomy quite like that of the Succomyidea. There are also well- 
developed internal cheek-pouches, shared, in a less degree however, by various 
American Muridea.* These pouches, as well as can be judged from alcoholic 
specimens, are relatively about as large as those of Tamas for instance. 
The body of Zapus is large behind, in correlation with the greatly-devel- 
oped posterior limbs, and tapers to the fore in a regular manner; the head 
being comparatively small, and there being no noticeable constriction of the 
neck. The head is conoidal, with a prominent and rather blunt snout and 
retreating under.jaw. The rather small eye is midway between the nose and 
ear. The upper lip is not visibly cleft, and is densely hirsute, with a fringe 
of hairs depending over and almost hiding the small front teeth. The naked 
muffle is of rather small size, and entirely inferior in position; above it, the 
hairy skin crosses with a deep transverse crease, forming a sort of imperfect 
overhanging flap, which is freely movable back and forth, even in alcoholic 
specimens, and looks as if it might be drawn down to partially cover the nos- 
trils. (I have observed much the same thing in Saccomyide.) ‘The nose-pad 
is impressed with a pair of median vertical grooves, and a transverse one is 
seen in some cases. The nostrils are completely lateral in position. The 
whiskers are rather sparse, but some of them are nearly half as long as the 
body. 
The structure of the external ear is rather remarkable (among Rodents) 
for the provision for perfect closure of the meatus, as in the Sorzcide for 
instance. The antitragus develops into a great flap, completely reversible, 
and capable of being applied against the meatus; and such, in fact, appears 
to be its usual position. The tragus, likewise, expands into a wide frill, or 
thin, free, rounded border, which ordinarily lies in apposition with the anti- 
tragal lobe opposite, completing the closure of the ear. On turning over 
these two flaps, the vestibule of the ear is seen to be of unusually large 
dimensions. The conch itself is of an ordinary contour, coming to a blunt 
*The presence of cheek-poucbes in the genus Hesperomys was first noted in 1880 by Gapper, who 
referred specimens of the common Hesperomys leucopus to Cricetus on this account, establishing a species 
C. myoides. In this matter, he was succeeded by Baird in 1857, who also recognized the pouches, and 
endorsed a Hesperomys myoides mainly upon this feature, failing, however, to observe that they also 
existed in other species of the same genus. At the same time that Mr. J. A. Allen announced the before 
unknown pouches of Zapus hudsonius, he also showed that they occurred as well in various species of 
Hesperomys ; and my subsequent dissections have satisfied me that pouches are present in all the North 
American species of Hesperomys proper ; i. e., the subgenus Vesperimus as established by me: Proc. Acad, 
Nat. Sci. Phila. 1874, 178. 
