OCR Text |
Show 90 ON A NEW DOLPHIN FROM BORNEO. [Feb. 1 9, although they have divided pterygoids, stating that he thinks it desirable to await the examination of the complete skeleton before placing them in the typical South-American genus Sotalia. All three differ from the present form by their much larger teeth ; while S.plumbeus aud S.perniger (gadamu) are further distinguished by their tall and falcate dorsal fins, and S. lentiginosis by its speckled skin. The other Indian form, S.frontatus, is a true Steno, with conjoint pterygoids and rugose teeth. There are also many other differences, such as variation in the number of teeth. As already mentioned, the specimen agrees with Sotalia and differs from Steno (exclusive of the Indian forms referred to that genus by Mr. Blanford) in the separation of the pterygoids. It further agrees with the former in the relatively large number of teeth and the smoothness of their enamel; Mr. True giving the number of teeth in Sotcdia as from 26 to 35, and in Steno from 20 to 27. In Sotalia the number of vertebrae varies from 51 to 55, of which 29 are precaudal; but in Steno the number is increased to 66, of which 35 are precaudal. In its 30 precaudals the present specimen agrees sufficiently well with Sotalia. It may therefore be taken that the specimen is not only referable to the last-named genus, but likewise to the typical Brazilian section of the same. The Indian forms (referred by Mr. Blanford to Steno) have been already differentiated, while the white Sotalia sinensis, in addition to its larger teeth, is readily distinguishable by its coloration. The South-American species, especially those from the Upper Amazons, are probably sufficiently distinguished by their geographical distribution, but a few words may be added in regard to them. Both Sotalia pallida and S. Jluviatilis, of the Upper Amazons, are broadly distinguished by the smaller number of their teeth, there being ^ in the former and |j in the latter. S.pallida further differs by the whitish colour of the upper-parts, while the peculiar distribution of the colours forms another point of difference in S. Jluviatilis. Comparison is more difficult in the case of the three forms respectively known as S. tucuxi, S. guianensis, and S. brasiliensis. The former of these is typified by two skulls in the British Museum from the Upper Amazons, the number of teeth in which is _, This form, if not identical with S. pallida, is probably very closely allied. Sotalia brasiliensis, from Rio de Janeiro, was described on the evidence of an immature specimen, and is said to be blackish above, with the sides fulvous, the belly white, and the flippers coloured like the back; the number of the teeth being =5. In many respects this form appears to come very close to the one uuder consideration. Sir William Flower was, however, of opinion that &. brasiliensis might prove to be the young of S. Jluviatilis. And apart from this, the figures given by Van Beneden (reproduced in pi. iii. of Mr. True's memoir) seem to indicate that the dorsal fin of |