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Show 1876.] A YOUNG DELPHINUS ALBIROSTRIS. 685 % The characters of the skeleton are almost identical in both. Thus the present specimen agrees with D. albirostris in the number of the vertebrae and in the peculiarities of the cervical vertebrae. There are, indeed, a few points of difference to be detected in the skull; but these are of minor importance and probably merely the differences of youth and age. The differences of import are to be found (1) in the character of the markings, (2) in the general shape of the body, (3) in the position of the dorsal fin. I consider, however, that the extreme youth of the specimen may account for the first two of these dissimilarities. The discrepancy in the markings is not great, and consists chiefly in the white patches on the side being more strongly pronounced and more distinctly separated by the black. Then as regards the difference of shape, we know that a massive head, or a head large in proportion to the rest of the body, is a peculiarity of youth in many animals. The position of the dorsal fin in relation to the middle vertical line, however, is a difficulty not so easily got over; we can scarcely suppose that as the Dolphin advances in age, the dorsal fin advances upon the back, at least to such an extent as to lie entirely in front of the middle vertical line. But the drawing of Van Beneden is the only guarantee that we have of its position in front of this vertical line ; and as we have already seen this to he in fault in one or two particulars, it is not improbable that it is in error in this respect also. I believe, therefore, that I am justified in regarding the Great- Grimsby Dolphin as a young specimen of the D. albirostris as described by Van Beneden. An interesting feature in the case, however, is the striking resemblance in external characters which this Dolphin presents to the D. acutus of Gray *. In both there is the same general outline of body, massive head, and humped appearance close to the tail; and in both the sides are piebald, the markings, however, differing in character. Here the similarity ceases; and in skeletal peculiarities they diverge widely from each other. TheD. acutus has 80 or 82 vertebrae; and in the cervical region the first four are ankylosed together, the first three completely, the fourth simply by its spinous process. In the Great-Grimsby specimen, as we have seen, the vertebrae numbered 90, and in the cervical region the atlas and axis alone were fused together. These characteristics, in conjunction with the white snout, are sufficient to show that the Dolphin I have described could not be considered referable to D. acutus. It will not be inappropriate to conclude this communication with a brief summary of the various localities in which the recorded specimens of D. albirostris have been captured; and in this way an idea of the geographical distribution of the species may be obtained. D. albirostris is a native of the North Sea, but is also found in * Gray, Spicil. Zool. 1828; Rasch, Nova Species Descripta cum tabulis ii. 1843; Duguid, Ann. and Mag. Nat. Hist. vol. xix. 1864; Schlegel, Abhandl. Zool. &c. 1841, tab. i. & ii. fig. 4, tab. iv. fig. 5. PROC. ZOOL. Soc-1876, No. XLV. 45 |
