432 ZOOLOGY. 
The latter might be identical with the species of South America. Fossil 
remains of the genus Manatus have been found in the tertiary deposits of 
North America. We possess but vague information respecting the fossil 
Manati of Europe. No one has been as yet satisfactorily determined. 
Fam. 8. Haticorip# The genus Halicore is distinguished from 
Manatus by the teeth, which are destitute of a root properly so called, by 
their plane upper surface, and by powerful, tusk-like incisors at the upper 
jaw, and «overed by the lips. The anterior limbs are uniform, and 
destitute of nails. The caudal is crescent-shaped, as in Cetacea. The 
nostrils are placed near the upper surface of the snout, and quite distant 
from its extremity. The inter-maxillaries and lower jaw are bent down- 
wards, another striking difference between this genus and Manatus, in 
which both jaws are nearly straight. HH. indicus, the only species known, 
inhabits the Kast Indian archipelago. 
Fam. 4. Rytinipz. The: genus Rytina is remarkable for the structure 
of the outer layer of the skin, which possesses below the thin and deciduous 
epidermis, a crust composed of fibres or tubes, placed vertically on the 
skin. This crust is so hard that steel can scarcely penetrate it, and when 
cut it resembles ebony by its compact tissue and its color. The entire 
surface is unequal, rough, cracked, and destitute of hairs. The lips are 
double, an internal and an external one. The jaws are provided on each 
side with a plate or compound tooth, destitute of a root, and resting on the 
jaws. There are no tusks. The caudal fin is crescent-shaped; the 
pectoral fins, or anterior limbs, have no nails externally visible. One 
single species is known, #2. borealis, inhabiting Behring’s island. It reaches 
twenty-four to twenty-five feet in length, and is therefore the largest of 
the living representatives of the family, and was only exceeded by the 
gigantic Dinotherium. 
Group 2. Trichechide. 
The Walruses constitute quite a peculiar group, hitherto placed near 
the seals on account of a general resemblance in the form of their body and 
in the similar structure of the limbs, which are four, the normal number in 
Vertebrata. In the head and teeth, however, they differ widely. There 
are neither incisors nor canines in the lower jaw, which is compressed 
anteriorly in order to pass between two enormous tusks, sometimes two 
feet in length, which project downwards from the upper jaw. The molars 
are all short, obliquely truncated cylinders; there are four of them on each 
side, above and below, but at a given age two of the upper ones fall off. 
The upper jaw possesses two deciduous incisors, which in form and struc- 
ture are similar to the molars. The walrus differs chiefly from Sirenidia 
by the presence of hind limbs, and short hairs covering the body, to which 
characters we may conveniently add the tusks. They have received the 
vulgar appellations of morse, horse-whale, sea horse, sea elephant, and also 
sea cow, now more restricted to Manat. 
636 
