The skull of these animals changes so much in form as the animal arrives at adult and old age that it is not always easy to determine the species by it, unless you have a series of them, of different ages and states, to compare. Thus Dr. Peters, in his revision of the genus after the publication of my Catalogue and figures of the skulls in the ‘Voyage of the Erebus and Terror’ and in the ‘Proceedings of the Zoological Society,’ formed no less than five species from the skulls of the southern Sea-lion (_Otaria jubata_)—_O. jubata_, _O. Byronia_, _O. leonina_, _O. Godeffroyi_, and _O. Ulloæ_,—referring the first four to the subgenus _Otaria_, and the last to _Phocarctos_ (see Monatsbericht, May 1866, pp. 265, 270). In his second essay, published a few months later (_ibid._ Nov. 1866), after his visit to London, he placed them all together in one subgenus (_Otaria_), and seems, by the way in which he has numbered four of them, to doubt their distinctness. It would have been better if he had at once simply reduced them to synonyms (as they must be reduced) and included with them _O. Ulloæ_, which is only the skull of a young specimen, such as was called _O. molossina_ by Lesson and Garnet. I may observe that I had shown in my first ‘Catalogue of Seals’ (1850), from the examination of the typical skull, that two or three of these nominal species were only very old or young skulls of the southern Sea-lion. It is the character of the Eared Seals or _Otariadæ_ to have a very close, soft under-fur between the roots of the longer and more rigid hairs. They are therefore called _Fur-Seals_ by the sealers, and are hunted for their skin as well as for their oil. The quantity and fineness of the under-fur differ in the various species; and the skin and under-fur bear a price in the market according to the country and the species from which they are obtained. Some species of the family have so little under-fur when they arrive at adult age, that they are of no value in the market to be made into “seal-skins;” these are therefore called _Hair-Seals_ by the sealers. They are only collected for the oil, as the skins are of comparatively little value. The skins of the Fur-Seal are much used in China, and are more or less the fashion in this country, sometimes being far more expensive than at others. The skins of the Hair-Seals are only used, like the skins of the Earless Seals or _Phocidæ_, for very inferior purposes, as covering boxes, knapsacks, &c.; but the animals are much sought after for the oil they afford.