MAMMALIA. 481 



points, as in the Plioca leptonix^ from the Australian seas, we have the sub- 

 genus Steiiorlujnchm. 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 Plioca monacha (the monk), from the Mediter- 

 ranean. When there are fo^r 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 Stemmatopus. 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 menaceil, 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 Macwrhinus, 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 Otaria 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 {0. ursina), eight feet long, is from the North Pacific Ocean. 

 Another species ( 0. juhata) is from fifteen to twenty feet in length ; found 

 in all the Pacific Ocean. 



Fossil remains of seals proper (Phoca) have be^ 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 ior 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 Europe, 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 o^ 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 



