224 FAMILY OTARIIDJE. 



ing a very broad interval between the first and second. The 

 first (in No. 15660) stands above the second permanent tooth ; 

 the second is just behind the third, while the fourth is a little 

 anterior to, but nearly over, tne fourth. In No. 6156 the milk 

 molars stand directly over the second, third, and fourth per- 

 manent ones. In several other young skulls, the third milk 

 molar is still in place, while all the others, except the canines, 

 have disappeared. Some of them were probably several weeks 

 old, showing that at least the canines are persistent for a con- 

 siderable period after birth. In two young skulls of CallorhinuSj 

 known to have been killed when between four and five weeks 

 old, the milk canines are still in place, and a trace remains of 

 the alveolus of the third superior milk molar. 



In all probability, the dental formula is the same in all the 

 Eared Seals, the incisors, except the exterior upper, disappear- 

 ing before birth. Of the molars the middle is smaller than the 



o 



others, while the third is longest persistent. The canines ap- 

 pear to remain for several months. 



IRREGULARITIES OF DENTITION, 

 i 



The Eared Seals seem to rather frequently present cases of 

 supernumerary molars, and more rarely cases of suppression of 

 molars. In respect to supernumerary molars, I am able to 

 record the following instances : In Callorhinus ursinus I have 

 noted the following irregularities : Skull No. 2922 (M. C. Z. 

 Coll.) has M. ^=|, the normal number being J=|; in another 

 (Nat. Mus. Coll., No. 11701), M. ^5; and in still others (M. C. 

 Z. Coll., No. 1787 ; N. M. Coll., 12270), M. |5f. In each case, 

 the identity of. the species is beyond question. In Zaloplms 

 calif ornianm = yiUespii, auct., I have noted the following: two 

 skulls (Nat, Mus. Coll., No. 15254; M. C. Z. Coll., No. 6162) 

 each with M. |^|, and one (M. C. Z. Coll., No.6163) with M. g,, 

 the normal number being M. |=|. In nearly every case the 

 supernumerary molars were as perfectly developed as the others. 

 About five per cent, of the skulls of these two species (of which 

 I have examined not less than thirty of each) present one or 

 more supernumerary molars. I have also found suppression of 

 molars in Arctoceplialiis australis (M. C. Z. Coll., No. 1131, 



~ X I 



The supernumerary molars are placed (in all the instances I 



