CHORDATA 



405 



relatively thick layer of fat. They may be divided into two 

 groups, the first comprising the walruses and the seals which 

 have ears, and the second the earless or true seals. 



The walruses have no external ears, and there is no free tail ; 

 the upper lip is provided with a fringe of stiff bristles, and the 

 body is covered with short, yellowish brown hairs. The canine 

 teeth in the upper jaw are elongated into large tusks, and these, 

 together with the hide and oil, are articles of commerce. An 

 adult male walrus is between three and a half and four meters 

 long. Their food is said to consist chiefly of Mollusca and sea- 

 weeds. There are two species of walruses, one in the Atlantic, 

 the other in the Pacific. The eared seals, unlike the walruses, 

 have no tusks ; there are two kinds, the sea lions, or hair seals, 



Fig. 389. Phoca vitulina, the harbor seal. (After Parker and Haswell.) 



and the sea bears, or fur seals. Both occur along the coasts 

 in the northern and the southern hemispheres in temperate 

 and cold waters, except in the North Atlantic, where they are 

 absent. The northern sea lion of the North Pacific is one of the 

 largest. They are gregarious and polygamous, each male 

 having from twelve to fifteen or more females. The most valu- 

 able fur seal is Callorhinus ursinus, the northern fur seal ; it 

 has a nearly black, silky under fur. The male is about two 

 meters in length, the female less. 



The earless or true seals have a shorter neck than the others, 

 and their appendages are not so well adapted to supporting the 

 body on land. They have no soft fur, but only stiff hairs. The 

 harbor seal, Phoca vitulina (Fig. 389), is the common seal of 

 the North Atlantic ; it is found also in the Mediterranean and in 



