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. 3. Haligorid.e. 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 covered 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 diiference between this genus and Manatus, in 

 which both jaws arc nearly straight. H. indicus, the only species known, 

 inhabits the East Indian archipelago. 



Fam. 4. Kytinid^. 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. Tlie caudal fin is crescent-shaped ; the 

 pectoral fins, or anterior limbs, have no nails externally visible. One 

 single species is known, R. 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. Trichechidce. 



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 eacli 

 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-ivhale, sea horse, sea eJephant, and also 

 sea cow, now more restricted to Manati. 

 636 



