36 BULLETIN OF THE 



ursinus already mentioned, the fangs of several of the molars have a 

 deep longitudinal groove on the outside, the fangs appearing to be 

 formed of two connate roots, but in the corresponding molars of the 

 other specimen there are no grooves, the fangs being wholly simple. 



Great variations in the form of the teeth and the bones of the skull 

 have also been pointed out as existing in several species of the P/tocidce.* 

 Naturalists are fast becoming aware of the fact that the bones of ani- 

 mals generally are not so invariable in form and proportions as formerly 

 supposed, and hence afford less reliable characters for the discrimination 

 of species than has been generally believed.f Such facts evidently 

 show that too high a value has been placed upon certain relatively 

 slight differences in the form of the teeth and certain parts of the skull. 



Color is one of the features commonly much relied on for the dis- 

 tinction of species among the higher vertebrates. In the case of the 

 Otariadce, as also happens in other groups, this feature proves to be in 

 no small degree unreliable. In respect to the hair seals, the three or 

 four best known species (Eumetopias Stelleri, Zalophus Gillespii, Z. 

 hiatus, and Otariajubata) eo closely resemble each other in color, and 

 different individuals of the same species at the same time vary so much 

 in this regard, that a description of the color of either of the species 

 is almost equally applicable to all. This is equally the case in the 

 fur seals, where sometimes specimens of such really widely distinct spe- 

 cies as the Callorhinus ursinus and the Arctocephalus falklandicus seem 

 hardly distinguishable in color.t 



Habits. 



In respect to general habits the eared seals seem to have much in 

 common that distinguishes them from the Pliocidce, at least so far as the 

 habits of the latter are known. All the species appear to assemble in 



especially an important paper by Dr. J. E. Gray, entitled " On the Variations 

 in the Teeth of the Crested Seal, C !t stopliora cristata," etc., Proc. Lond. Zool. Soc., 1849, 

 pp. 00-03. Also, by the same author, another entitled " Notes on Seals {Pliocidce) and 

 tin- Changes in the Form of their Lower Jaw during Growth," Ann. and -Mag. Nat. 

 Hist., 4th Series, Vol. IV, pp. 342 -346, November, 1869. 



i See " Mammalia of Massachusetts," Bulletin Mus. Comp. Zool., Vol. I, pp. 143- 

 252, October, 1869. 



J In respect to a skin of C wsinvs from California, Dr. Gray has remarked: "The 

 skin is so like that of Arctocephalm nigrescens [= falklandicus] that we were induced to 

 regard it as a second specimen of that species before we received the skull." (Catalogue 

 Of Seals and Whales, p. 52.) 



