COUES ON GEOMYS AND THOMOMYS G. BURSAEIUS. 223 
flat ; the sides rapidly converge ; the under side and mouth parts are anom 
alous in their peculiar configuration. The muffle is entirely hairy, excepting 
a small, definitely naked nose-pad, somewhat T-shaped, with long arms and a 
short leg ; the nostrils opening obliquely between these. There is a consid 
erable hairy interval between this pad and the incisors, and a fringe of long 
hairs hangs down over these teeth. The upper incisors appear to be situ 
ated remote from the mouth ; for beneath them is a long strip of finely furry 
skin, longitudinally vaulted, with sides sloping upward to a median line, like 
the roof of a house with its ridge. This great space, near an inch long, 
bounded on either side by the swollen furry ridges which constitute the 
external lips, leads to the contracted orifice of the mouth proper, or that part 
of the buccal cavity lined by mucous membrane, to which the parts just 
described are merely the vestibule. The mucous membrane only comes to 
the border of the thick external lips in a small patch on each side. The lip 
laps loosely around the base of the under incisors, and the opposite sides meet 
behind the teeth. In fact, the curious conformation is such that the mouth 
actually shuts sideways by approach and meeting of the thick lips from either 
side ; further closure of the jaws resulting in merely a folding back of the thus 
apposed lips. When the mouth is closed, the incisor teeth are entirely shut 
out of the buccal cavity, and surrounded behind, as well as elsewhere, by 
furry integument ; in a large specimen, with the tips of the incisors in appo 
sition, the end of one's finger may be passed behind them, yet not into the 
mouth at all. On wrenching open the jaws, the fleshy tongue is seen largely 
filling the remarkably contracted true orifice of the mouth ; but so constricted 
is the opening that the molar dentition can scarcely be brought into this 
view. This particular condition of the parts is probably not met with outside 
the present family. 
The pouches of this species at first supposed to be pendulous bags 
hanging from the mouth, then with some correction found to be not pendu 
lous, yet believed to open into the mouth -from within are wholly external, 
and have^p more connection with the buccal cavity than the belly-pouch of 
a kangaroo or opossum has to do with the genital organs. These sacs are 
simply a purse-shaped duplicature of the loose skin of the side of the head 
and neck. The free margin of the pouch arises from the side of the upper 
