4 7 2 Bulletin American Museum of Natural History. [Vol. XVI, 



two series. In all of the Pacific coast skulls that have the 

 general appearance of being female the lower molar has only 

 three cusps, while all the skulls that are apparently male 

 have four, as in the Atlantic coast form. Thus in No. 9480 

 (Nat. Mus.), from Kenai, No. 21476, from St. Michaels, and 

 No. 6486 from Washington the lower molar has four cusps, as 

 in male skulls from the Atlantic coast. The premolars are 

 also all similar in the two series, except for the larger size of 

 the teeth of the males, in both series. This is contrary to Dr. 

 Merriam's discovery (as reported by Dr. True, /. c.), that: 

 "In P. vitulina the lower premolar [ = premolars ?] and molar 

 have usually four cusps each, but in the Pribilof seal three." 

 A large fully mature skull from the Pribilof Islands (Nat. 

 Mus. No. 49550), apparently a female, and probably one of 

 the skulls examined by Dr. Merriam, agrees with the sup- 

 posed female skulls from St. Michaels. In another Pribilof 

 skull, from St. George Island (Nat. Mus. No. 101330), also 

 without indication of sex but apparently a male, the lower 

 molar has four cusps, as in Phoca vitulina. 



In a very old heavily ossified skull (Mus. Comp. Zool. No. 

 6157) from Santa Barbara Islands, evidently a male, the right 

 lower molar has four cusps, and the left lower molar three, 

 with the fourth distinctly indicated but very small. 



In a series of four skulls from Bering Island, collected by 

 Dr. Stejneger, unmarked as to sex, three of which are very old 

 and the other quite immature, the lower molars in all of the 

 old skulls are distinctly 4-cusped ; in the young skull the left 

 lower molar is just as distinctly 3-cusped, while the right lower 

 molar is 4-cusped! (See Fig. 9, p. 490.) Also, in four skulls 

 (received since the above was put in type) from San Geronimo 

 Island, L. Cal., two of which are male and two female, the 

 number of cusps on the lower molar varies in both sexes and 

 also on the two sides of the same jaw from three to four. 



The relative size and mode of implantation of the teeth in 

 the jaws (both upper and lower) is the same in specimens 

 from the west coast of North America as in those from the 

 east coast, with the same great sexual difference in size, and 

 in the position of the teeth in the jaw. 



