98 
GENUS APLODONTIA.— Rich. 
DENTAL FORMULA. 
Incisive | ; Canine jj— ; Molar ~ — 22. 
Incisors, very strong, flatly convex anteriorly, without grooves, narrower 
behind. Molars, simple, remarkably even on the crowns. The'first in the 
upper jaw, small, cylindrical, and pointed, is placed within the anterior 
corner of the second one, and exists in the adult. The rest of the molars 
are perfectly simple in their structure, without roots, and have slightly 
concave crowns, which are merely bordered with enamel, without any 
transverse ridges or eminences. On the exterior side of the four posterior 
pairs of upper molars, and the inner side of all the lower ones, there is an 
acute vertical ridge extending the whole length of the tooth, formed by a 
sharp fold of enamel. When the molars are in situ, there is a wide semi- 
circular furrow between each pair of ridges, formed by the two adjoining 
teeth ; the side of each tooth opposite the ridge is convexly semicircular. 
The second grinder in the upper jaw, and the first in the lower one, are a 
little larger than the more posterior ones, and the former has a projection 
of enamel at its anterior corner, producing a second though smaller vertical 
ridge, within which the first small molar is situated leaning towards it. 
There is a slight furrow on the exterior sides of the lower molars, most 
conspicuous in the first one. 
Palate, narrow, bounded by perfectly parallel and straight rows of 
molars. 
Head, flat and broad ; nose, a little arched, thick, and obtuse. Lower 
jaw, thick and strong, with a large triangular process, concave behind, 
projecting at its posterior inferior angle further out than the zygomatic 
arch. The transverse diameter of the articulating surface of the condyle 
is greater than the longitudinal one. The jaw is altogether stronger than 
is usual in the Rodentia. 
Cheek-pouches, none ; eyes, very small ; ears, short and rounded, 
approaching in form to the human ear, and thickly clothed with fur like 
that of a muskrat, but not so long or fine. Limbs, robust, short ; feet, 
moderately long, with naked soles ; five toes on all the feet, rather short 
but well separated ; the thumb of the fore feet is considerably shorter than 
the other toes ; claws, particularly the fore ones, very long, strong, much 
compressed, and but little curved. 
