226 



FAMILY OTARIID^. 



considerable range of individual variation in representatives 

 of the same species, so that coloration alone fails to afford sat- 

 isfactory diagnostic characters. All the Fur Seals are black 

 when young, but they become lighter with age, through an 

 abundant admixture of grayish hairs which vary from yellow- 

 ish-gray to whitish-gray. The southern Fur Seals are generally, 

 when adult, much grayer than the northern. There is hence a 

 wide range of color variation with age in the same species, as 

 there is also among conspecific individuals of the same sex and 

 age. While some have the breast and sides pale yellowish-gray, 

 others have these parts strongly rufous, the general tint also 

 showing to some extent these differences. 



There is also a wonderful disparity in size between the sexes,* 

 the weight of the adult males being generally three to five 



* The sexual difference in size varies only slightly in the different genera ; 

 it is greatest, apparently, in Otaria, and least in Arctocephalus. It is very 

 much less in Arctoceplialus australis than in the northern Fur Seal ; while 

 relatively small in Zaloplius, it is very great in both Otaria and Eumeiopias. 

 In Otaria jubata, the average dimensions of eight old male skulls are, length 

 350 mm., breadth 223 mm.; of four old female skulls, length 261 mm., breadth 

 143 mm. In JEumctopias stelleri the average length of ten old male skulls is 

 375 mm., breadth 221 mm. ; of two old female skulls, length 296 mm., breadth 

 157 mm. In Zalophus californianus very old male skulls obtain a length of 

 290 mm. to 330 mm., while very old females reach 220 mm. to 237 mm. Five 

 old male skulls average, length 269 mm., breadth 157 mm; five old female 

 skulls, length 219 mm., breadth 103 mm. In Arctocephalus australis two old 

 male skulls average, length 260 mm., breadth 145 mm., two old female 

 skulls, length 230 mm., breadth 121 mm. In CalJorhinus ursinus eight adult 

 male skulls (not generally very old) average, length 243 mm., breadth 123 

 mm. ; four female skulls of nearly corresponding age average, length 188 mm., 

 breadth 96 mm. These data may be tabulated as follows, 100, in the column 

 of "Approximate ratio," representing the male sex : 



