494 Bulletin American Museum of Natural History. [Vol. XVI, 



described in their large size and heavy dentition in comparison 

 withftrue Phoca richardii from further north, and with the 

 Pribilof Islands skulls. They present no other very appre- 

 ciable differences than greater massiveness in general struc- 

 ture and dentition. The lower molar is 3-cusped in both 

 rami of one of the males, and faintly 4-cusped on the left 

 side and 3-cusped on the right side in the other; in one of 

 the females the lower molar is 4-cusped in both rami, and in 

 the other 4-cusped on the right side and 3-cusped on the left 

 side showing, if further evidence were needed, that the 

 variation in the number of cusps in the lower molar is a 

 feature merely of individual variation and not a sexual, and 

 much less a specific character. 



Phoca richardii differs from Phoca vitulina from the east 

 coast ( = P. concolor Dekay) of North America only in the 

 slightly greater posterior prolongation of the premaxillae, giv- 

 ing them a slightly more extended contact with the nasals ; this 

 feature, while somewhat variable, will suffice to distinguish 

 the two forms at a glance. In the general conformation of the 

 skull and in dentition the two forms are indistinguishable. 



Phoca richardii differs from Phoca stejnegeri through the 

 much smaller size and much less massive character of the 

 skull, as shown in the table of measurements (p. 498), where, 

 in a note to the table, attention is called to strictly com- 

 parable specimens of the two 

 forms . The auditory bullse , for 

 example, in No. 21311, from 

 Bering Island, a very young 

 skull with all the sutures open, 

 are twice the size of the audi- 

 tory bullae in No. 15276, from 

 the Pribilof Islands, a very old 



Fig. 10. Comparative views of right audi- . .. .. r , 1 



tal bulla of Phoca stejnegeri and Phoca rich- skull With the CrOWnS of the 

 ardii. a, P. stejnegeri, U. S. Nat. Mus. No. , .... 



21311, youne female (?), probably less than a teeth almost Wholly WOm away, 



year old ; J, P. rickardii, U. S. Nat. Mus. _. . , 



No. 6486, a 'young adult' female. Phoca OChoteHSlS haS a SKUll 



so much slighter in structure 



and so different in proportions and dentition from P. richardii 

 that no comparison of the two is necessary. 



