A p l o d o n t i a . (Richardson.) S e w e l l e l ,
Aplodontia.' Richarbson, -Zool. Joum. January, 1819.
C H A R A C T E R S .
Dental formula ; incisors §, canines $=&, grinders £=§ = 22.
Incisors, very strong, flatly-convex anteriorly without grooves; narrower behind. Grinders
simple, remarkably even on the crowns. The first in thè 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 grinders 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 thé four posterior pairs of upper grinders, 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 grinders are in situ, there is a wide
semicircular 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, producinga second though smaller vertical
ridge* within which the first small grinder is situated and leans towards it. There is a slight
furrow on the exterior sides of the lower grinders, most conspicuous in the first one.
Palate narrow, bounded by perfectly parallel and straight rows of grinders. .
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 on both sides with short hair.
Body thick and short, clothed .with fur like that of a musk-rat, but not so long or fine.
Limbs robust, short; feet moderately strong, 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.
Tail very short, concealed by the fur of the hips. Mamma six, the anterior pair situated
between the fore-legs.
Habits.—Animals forming small societies, feeding on vegetable substances* and living in
burrows.
* Mr. David Douglas.