324 CALLORHINUS URSINUS NORTHERN FUR SEAL. 



TEETH. The dentition is relatively much weaker than in 

 either Eumetopias or Zalophus, or even in Arctocephalus. As 

 usual in the Otaries the outer pair of upper incisors is much 

 larger than the others and caniniform ; the two central pairs 

 are flattened antero-posteriorly, and in youth and middle age 

 their crowns are deeply divided by a transverse groove. The 

 lower incisors are smaller than the upper and are hollowed on 

 their inner face but are not grooved. The canines are large 

 and sharply pointed, the lower somewhat curved. The molars 

 are small and closely approximated, with sharply conical crowns 

 and all single-rooted. They have no accessory cusp, or only 

 very minute ones in early life. The roots are usually grooved 

 both externally and internally, sometimes slightly so, but some- 

 times so deeply that the fang seems to consist of two connate 

 roots. The distinctness of these grooves varies not only in dif- 

 ferent individuals, but in the corresponding teeth of the two 

 sides of the mouth in the same skull,* so that it is not improb- 

 able that teeth may be found in which the grooves of the fangs 

 may be entirely obsolete, or so deep as to nearly or quite divide 

 the fang into two distinct roots. The roots of the molars are 

 very short, and but partly fill their alveoli ; hence when the 

 periosteum is removed they fit so loosely that they require to be 

 cemented in to prevent their constantly falling out whenever 

 the skull is handled. The canines and the incisors have much 

 longer roots, which more nearly fill their sockets. 



SKELETON. Vertebral formula : Cervical vertebrae, 7 ; dorsal, 

 15 ; lumbar, 5 ; sacral, 3 ; caudal, 8 to 10. 



The skeleton hi its general features resembles that of Eume- 

 topias stellerij already described. The bones of C. ursinus are, 

 however, all slenderer, or smaller in proportion to their length, 

 than in that species, the general form of the body being more 

 elongated. The -scapulae are shorter and broader than in E. 

 stelleri, the proportion of breadth to length being in the one as 

 11 to 10 and in the other as 13 to 10. The pelvis is more con- 

 tracted opposite the acetabula in C. ursinus than in E. stellerij 

 and the last segment of the sternum is also longer and nar- 

 rower. The differences in the skull of the two forms have 

 already been pointed out in the generic comparisons. In pro- 

 portions, the principal difference, aside from that already men- 

 tioned as existing in the form of the scapula, consists in the 



* See Bull. Mus. Comp. Zool., vol. ii, pi. ii, figs. 6 & and 7 e. 



