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Show 1881.] PROF. W. H. FLOWER ON THE ELEPHANT SEAL. 161 lopment of the canine teeth, as can be well seen in the figures of the type skull of the female M. angustirostris, as given by Allen. On comparing the upper surface of this with a series of male skulls, it will be seen that the difference consists chiefly in the extent to which the maxillae project beyond the sides of the prsemaxillse, which in the former is almost nil, and in the latter very considerable, to allow room for the roots of the great canines on each side of the preemaxilla). Even in the youngest skulls this difference in the sexes is seen. The variations in the proportion of the breadth of the rostrum measured at the middle, halfway between the nasal orifices and the ends of the prsemaxillse, in different specimens, are shown in the following table:- Very young female, No. 3934, Mus. Koy. Coll. Surg The type sjDecimen of M. angustirostris (according to Allen's fig.), Very young male, No.3934 A. Mus. Eoy. Coll. Surg '. 1 Adult male, No. 3920, Mus. Roy. AdCuolllt. mSaulreg, No. 3921, Mus. Eoy. Coll. Surg Adult male, No. 3921A i T ,, P '• Breadth of L e f * °f middle of skull. , mm. rostrum. 204 233 437 463 564 mm. 46 59 144 154 176 Proportion, length of skull being 100. 22-5 24-3 25-3 33-0 333 31-2 There is certainly one character by which the type specimen of M. angustirostris, judging from Gill's description and Allen's figure, differs from any of the skulls of southern Elephant Seals with which T have compared it. This is the shorter antero-posterior extent of the palate-bones, and the deeper emargination of their hinder border. Before this distinction can be accepted as a specific character, it should be known whether it is constant. There is much variation in the size of the palate-bones of the southern forms : the leno-th from before backwards between the palato-maxillary suture in the middle line and the spine in the large skull No. 3921 is but 35 millims. ; in the somewhat smaller skull, No. 3920, the same distance is as much as 51 millims.; and in the largest skull (No. 3 9 2 1 A ) it is 65 millims., therefore about double that of the skull which conies nearest to it in general size. When the idea prevailed that each species was separately created in the region which it inhabits, geographical reasons were stronger than now for assigning specific distinction. But Allen fully admits, indeed suggests himself, that the two presumed species, though long isolated, have been derived from one stock, "the southern being an PROC. ZOOL. S O C - 1881, No. XI. 11 |