604 PHOCA FQETIDA RINGED SEAL. 



bled coloring usually characterizing the adults not being at- 

 tained till the second or third year. The sexes vary in size, as 

 already noted, the female being considerably the smaller. This 

 difference of size is well shown in the measurements of the 

 skulls given below. Aside from the skull of the female being 

 smaller than that of the male, its structure is weaker, the sur- 

 face less roughened for the attachment of muscles, the muzzle 

 narrower, the teeth smaller, and the lower jaw much slenderer. 

 In the series of skulls collected by Mr. Kumlien, which were 

 carefully marked for sex, the old males have an average length 

 of about 186 mm., and an average breadth of about 115 mm., 

 while the same dimensions in the old females are respectively 

 168 mm. and 108 mm. 



In genera], skulls of the same sex and of corresponding ages 

 Tary considerably in details of structure and proportion, but 

 the only purely individual variations worthy of special com- 

 ment are exhibited in the teeth, which are surprisingly variable 

 in respect to size, and in the number and shape of the acces- 

 sory cusps. That these variations are not due to age and the 

 accidents of attrition is shown by the fact that they are as well 

 marked when the teeth first cut the gum as at later stages. 

 The last upper molar is especially variable in size and in the 

 prominence of the cusps, the accessory cusps being sometimes 

 well developed and again almost wholly obsolete. The last upper 

 molar has usually only two points, the posterior of which is 

 small, but there is occasionally another still smaller on the an- 

 terior inner border of the tooth. Generally the other upper 

 molars have each three cusps, of which the anterior is the 

 smallest, and frequently is wholly obsolete on the second molar 

 when the third, fourth, and fifth molars are each 3-pointed. 

 Frequently, however, all the upper molars, except the first, are 

 4-pointed, while in a nearly equal percentage of the skulls ex- 

 amined the molars are all only 2-pointed, or all, except the 

 third, which may be 3-pointed. Sometimes the third or fourth 

 upper molar is 3-pointed, while the others are 2-pointed.' In 

 one skull all are 3-pointed, including even the first. 



The lower molars are less subject to variation in respect to 

 the number of points, they being almost invariably 4-pointed, 

 except the first, which is usually 3-pointed. The chief varia- 

 tion I have noticed is that the fifth is sometimes only 3-pointed, 

 like the first, while the first is sometimes 4-pointed, like the 

 others. The size and shape of the cusps vary greatly, being 



