RODENTIA. 151 
B. hottentottus, Less. and Garn., Voy. de la Coquille, pl. ii. 
(The Hottentot Rat-Mole.) Smaller; grey; incisors smooth ; 
hardly as large asa Rat. The 
Gromys, Rafin.—PsEuposroma, Say.—Ascomys, Lichten. 
Which have four compressed prismatic molars throughout; the 
first double, the remaining three simple; the upper incisors furrowed 
with a double groove in front ; five toes to each foot; the three 
middle anterior nails, that of the medius particularly, very long, 
crooked, and trenchant. They are low animals, and have very deep 
cheek-pouches, which open externally, enlarging the sides of the 
head and neck in a singular manner. One species only is known, 
G. bursarius 3 Mus bursarius, Shaw.(1) (The Canada Ham- 
ster.) Size of a Rats;‘fur of a reddish grey; tail naked, 
and but half the length of the body. Inhabits deep burrows in 
the interior of North America. — 
DipeLostoma, Rafin. 
The Diplostome are almost precisely similar to the Geomys, but 
they have no tail.(2) 
These animals are also from North America. ‘The species 
before us is reddish, and ten inches in length. 
We now pass to larger Rodentia than those of which we 
have hitherto spoken, but of which several still have well 
defined clavicles. Of this number is the 
Castor, Lin. 
The Beavers are distinguished from all other Rodentia by their 
horizontally flattened tail, which is nearly of an oval form, and 
covered with scales. ‘They have five toes to each foot: those of the 
hinder ones are connected by membranes, and that next to the thumb 
has a double and oblique nail. Their grinders, to the number of 
four throughout, and with flat crowns, appear as if formed of a 
doubled bony fillet, or so as to show one sloping edge at the internal 
- 
(1) The figures of this animal, first published Trans. Lin. Soc. Vol. V, pl. viii, 
and Shaw, Vol. II, part I, pl. 138, represent it with the internal skin of the 
cheek-pouches turned inside out, as though it had two sacs to the sides of the 
head. There is nothing like it in nature. It is well represented, Acad. Berlin, 
1822 and 1823, pl. ii. 
(2) M. Rafinesque describes them as having only four toes to each foot. The 
European species has five, like the Geomys. 
