DISTINCTIVE CHARACTERS. 



569 



of the pelvis is precisely that of the tibia, being respectively 

 200 nun. aud 255 inm. P. fcetida presents a different ratio, 

 due not to the shortness of the pelvis so much as to the great 

 length of the tibia, the tibia measuring 190 mm. and the pelvis 

 170 mm. 



Not only is the dentition exceptionally heavy in P. vitulina, 

 but the whole skull is ponderous, in striking contrast with the 

 light thin skull of either of the other species. In other words, 

 P. vitutina is a big-headed, short-bodied, and short-limbed spe- 

 cies. While the linear dimensions of old male skulls fully equal 

 or somewhat exceed the same measurements of equally old 

 male skulls of P. grosnlandica, the length of the limbs, and also 

 the entire skeleton, is much less, as shown by the following 

 measurements : * 



Including scapula. 



t Adult male. 



J Adult female. 



The fore limb, as well as the total length of the animal, is 

 even actually shorter than in P. fcetida, although the latter is a 

 much smaller animal. The ratio of the length of the skull to 

 the length of the whole skeleton in the three species in ques- 

 tion is as follows : in Phoca ritulina, as 1 to 5.6 ; in Phoca grcen- 

 landica, as 1 to 8 ; in Phoca fostida, as 1 to 8.6. Measurements 

 (in millimeters) of the principal parts of the skeletons of these 

 three species are presented in the following table, from which 

 it will be seen that the shortness of the caudal vertebrae in 

 Phoca vitulina is also a noteworthy point. This is due in part 



* The largest skull of P. vitulina in a series of ten measures 223 rum. iu 

 length and 144 mm. in extreme breadth, while the largest skull of P. grcen- 

 landica iu a series of twelve measures 228 mm. in length and 133 mm. in 

 breadth. No other in the series, however, exceeds a length of 220 mm. or 

 a breadth of 128 ruin., old skulls of P. vitulina averaging the longer, with 

 the breadth very much greater. 



