330 CALLORHINUS URSINUS --NORTHERN FUR SEAL. 



the toe-flaps of the posterior limbs, which in C. ursinus are 

 greatly developed, their extension beyond the digits being 

 nearly equal to the length of the rest of the foot in adult 

 females 140 mm. beyond the toes. In Arctocephalus australis: 

 (= falMandicuSj auct.), on the other hand, they extend, as in 

 most of the other Otaries, only a short distance beyond the 

 toes, the indentations between them being but little posterior 

 to the ends of the toes. 



The extremes of sexual variation seem to be presented by 

 Callorhinus ursinus and Arctocephalus australis; the former 

 presenting the greatest and the latter the least amount of sex- 

 ual variation in size of any of the five American species of 

 Otaries, to which my comparisons are limited by lack of mate- 

 rial. The adult males of these two species differ little in size, 

 while the female of Arctocephalus australis is very much larger 

 than the female of C. ursinus. The average length of the 

 skull in the adult males of both species is about 245 mm. ; of 

 the females of A. australis about 233 mm., against 185 mm. 

 in C. ursinus. 



For purposes of comparison I submit the following measure- 

 ments of skulls of A. australis for corresponding measurements 

 of C. ursinus (see antea, p. 323) : 



