MAMMALIA. 481 
points, as in the Phoca leptonix, from the Australian seas, we have the sub- 
genus Stenorhynchus. The sub-genus Pelagus has four incisors above and 
four below associated to grinders with obtuse cones, with a slightly marked 
heel before and behind, as in Phoca monacha (the monk), from the Mediter- 
ranean. When there are four incisors above and only two below, the 
molars or grinders compressed, slightly trilobate, and supported by thick 
roots, the species belong to the sub-genus Slemmatopus. The hooded seal 
(Ph. cristata), which is an example of the last sub-genus and an inhabitant 
of the Arctic Ocean, has been noticed on the shores of New England. It 
is seven or eight feet long; possesses a piece of loose skin on the head, 
which can be inflated at the pleasure of the animal, and is drawn over the 
eye when it is menaced, at which time the nostrils also are inflated like 
bladders. Lastly, when the incisors are four above and two below, but the 
molars obtuse and conical, and the snout resembling a short movable pro- 
boscis, the sub-genus is called Macrorhinus, to which the largest known 
seal (Phoca leonina) must. be referred. This is the sea-lion, or sea-wolf, 
or sea-elephant of the various writers. It is from twenty to twenty-five 
feet in length. Common in the northern latitudes of the Pacific Ocean. 
It constitutes an important object of the fisheries, on account of the oil 
which it yields abundantly. 
The genus Otarta is composed of seals with external ears, and besides 
the four superior middle incisors have a double cutting edge, a circumstance 
hitherto unknown in any animal; the external ones are simple and smaller, 
and the four inferior, bifurcated. The molars are simply conical, and the 
toes of the fore feet almost immovable; the membrane of the hind feet 
lengthened out into a slip behind each toe; all the nails are flat and slender. 
The sea-bear (O. wrsina), eight feet long, is from the North Pacific Ocean. 
Another species (O. jubata) is from eae to twenty feet in length; found 
in all the Pacific Ocean. 
Fossil remains of seals proper (Phoca) have ‘te discovered in the 
tertiary beds of Europe, and referred to three different species, with others 
not yet determined. 
There is also a form found in Germany which differs more widely from 
the seals proper, and for which the genus Pachyodon has been proposed, 
the full characteristic of which has not as yet been made known. 
The genus Phocodon is another extinct genus, peculiar to North America 
and Kurope, which, when first discovered among us, was described as a 
gigantic reptile, and received the name of Basilosaurus. Subsequently it 
was found, by the structure of its teeth and the manner in which the latter 
were implanted in the jaw, to belong to the class of Mammalia, and to come 
near the aquatic tribe. By some, however, it is erroneously placed among 
herbivorous cetaceans. The general character of the teeth reminds us of those 
of the seals (Phoca), whence the name of Phocodon. They have also the 
external appearance of the teeth of some sharks, and the name of Squalodon 
was suggested for them by a French naturalist, who had found some of 
them in the tertiary deposits of Bordeaux. Zeuglodon is another appella- 
tion for these remains, alluding to the structure of the teeth. One species 
685 
