MKKI-Tir VARIATION. [I-AKT I. 



premaxilla- is different from that seen in other specimens of Phoca, 

 and, doubtless in correlation with the absence of the two upper 



C 

 FIG. .",1. Incisors ami canines of 1'lioca barbata, No. 318. 



incisors, the width of the premaxilla? is considerably less than in 

 -p. cimens having the normal dentition. B. M., 90. 8. 1. 6. 

 310. P- barbata: in left upper jaw are three normal incisors; but 

 on the right side- the incisors have been lost. The alveoli, however, 

 shew plainly that only two incisors had been present. Of these 

 tin- outer one in size agrees with &, being a large alveolus equal to 

 that "| , df the other side, but the second alveolus, occupying the 

 place of j 7 " 1 and /-, is also a large alveolus, scarcely smaller than that 

 for P. It appears therefore that in this specimen a single large 



t oot h st 1 in place of i l and i~. A lower jaw placed with this skull 



was normal, but it was not certain that it belonged to the skull. 

 O. M., 1724. 



Premolars and Molars. 



Normal urninf/einent. In Phocid;e there are normally rive 

 teeth behind the canines in each jaw, and according to the received 

 accounts, of these teeth 4 are preinolars and one is a molar, giving 

 /> ;}, in j, Tin 1 Otariida 1 on the other hand have generally p^, m^, 

 but Imtli the two upper molars stand at a level behind that 

 of the lower molar, so that the posterior molar, ^ is placed so 

 far back that it meets no tooth in the lower jaw. Some of the 

 ( Mariid;e. however, as 0. cul (/'<>riii<nt<i, do not possess such a pos- 

 terior tooth, and have only m\. 0. stelleri is peculiar in the fact 

 that it also has only one upper molar, but this tooth is separated 

 by a large diasteina from y 1 , and stands in the position character- 

 istic '"' of the other ( Hariida'. Hence it may be supposed that 'w 1 

 i- really aliment while m* is present. 



Amongst the eases will be found some of the presence in Pho- 

 eid;e, especially Halichoerus, of an extra molar placed in the usual 

 position ,,(' 1,1^ in the < Mariidii'. But lest any one should think it 

 manifest that this is an example of Reversion to the Otarian con- 

 dition, at tent ion is called to cases of such an extra molar in the 

 Otariida 1 also. Similarly there are instances of absent molar in 

 those OtariidsB which have /// j, leaving m ] : and of these cases one 

 occurs in such a way as to leave the peculiar diasteina between 



