98 Mr. Bnooxzs on a new Genus of the Order Rodentia. 
as scarcely to be capable of scientific description, is strongly 
opposed to the very simple form of those of Lagostomus, which 
present only three parallel lines of enamel, separated by two 
intervening portions of the osseous part of the tooth. 
The rami of the lower jaw are arched, broad, and strong, and 
exhibit very distinctly on their under surface the roots of the 
molar teeth, and also the course of the incisors within the bone: 
the angle is very much produced posteriorly : the plate is broad, 
and is deeply grooved above, behind the molar teeth: the co- - 
ronoid process is very acute ; the condyle elongated from before - 
backwards, and the glenoid cavity large, and extended con- 
siderably in the direction of the condyle. 
As all the Mammalia have seven cervical vertebrz, with the 
exception of the Sloth, which has nine, there cannot be any : 
necessity for referring to those bones for numerical comparison 
with those of other animals. The number of ribs, and con- 
sequently that of the dorsal vertebre, is twelve on each side ; 
that of the lumbar, seven: in both these particulars Lagostomus - 
agrees with the Jerboa. The sacral vertebra of Lagostomus are 
three, and the caudal twenty. | 
The anterior extremity is comparatively shorter than in the 
greater number of the Rodentia, but is longer and stronger than 
in the Jerboa. The clavicle is complete. The scapula is rather 
delicate ; its spine is but slightly elevated ; and the acromion is 
slender, flattened, and considerably elongated, equalling in length 
the remaining portion of the spine. The os brachii is strong, has 
a considerable tubercle at its outer surface somewhat below the 
head of the bone, and exhibits a tendency to expand into a : 
ridge (the processus deltoides). The condyles are lengthened 
transversely, and are widely separated. The radius is about 
one-fourth longer than the os brachii, and it inclines towards 
the ulna, which is anchylosed anteriorly with it through about 
two- 
