566 PHOCA VITULINA HARBOR SEAL. 



have the cingulum smooth, while in P. vitulina it is more or 

 less distinctly beaded (sometimes striated) on the anterior por- 

 tion of the inner side, especially in early life, and on the three 

 anterior teeth. In old age, however, this feature often becomes 

 wholly obliterated. The oblique position of the teeth in the 

 jaw evidently results from their large size, the space for their 

 reception being too short to permit of their standing end to end 

 in the usual manner. Their large size also results in, or neces- 

 sarily accompanies, a considerable modification of the whole 

 facial portion of the skull, which is greatly thickened and 

 broadened, in comparison with the same part in the other above- 

 mentioned species. Passing to the palatal region, P. vitulina 

 and P. fcetida present an essential agreement, the posterior 

 nares in both being rather abruptly narrowed posteriorly ; the 

 hind border of the palatines is deeply hollowed, and the narial 

 septum is imperfectly developed at its posterior border. In P. 

 fcetida it remains wholly unossified behind the palato-maxillary 

 suture, except the buttress-like extensions along the narial roof 

 and floor, and ossification of the septum is carried but little 

 further in P. vitulina. In P. grcenlandica, however, the septum 

 is fully and even heavily developed to the very end of the 

 squarely truncated hind border of the palatines, dividing verti- 

 cally the posterior narial opening, which is scarcely at all con- 

 tracted, into two distinct passages. Its transverse breadth is 

 nearly twice its vertical width, while in P. vitulina these dimen- 

 sions are nearly equal. 



The auditory bulla3 differ considerably in form in each of the 

 three species here compared. In general form they have in 

 each the outlines of a nearly equilateral triangle, but the sides 

 are set in each at a different angle relatively to the transverse 

 axis of the skull. In P. fcetida the anterior border is nearly 

 parallel with the plane of this axis ; in P. vitulina the two form an 

 acute angle, while in P. grcenlandica they form nearly a right 

 angle. The anterior face of the bullse is nearly plane in P. 

 fcetida, strongly hollowed in P. grcenlandica, and slightly so in P. 

 vitulina. In both P. fcetida and P. grcenlandica the lateral ex- 

 tension forming the lower border of the meatus auditorius is 

 depressed and swollen or rounded below, forming an abruptly 

 constricted neck to the bulla proper, but in P. vitulina it slopes 

 evenly from the highest part of the bulla and terminates in a 

 uniformly tapering triangular point. 



The facial portion of the skull, as already intimated, is broad 



