| OCR Text |
Show 1869] MR. G. BUSK ON FOSSIL REMAINS FROM BORNEO. 413 nary fossil or extinct forms, all except R. etruscus. All the other characters, moreover, would equally exclude these species ; I shall, therefore, at present advert only to the latter three above named. Fig. 4. Grown surface. 1. If we regard the entire dentition of Rhinoceros sondaicus*, it is of course at once distinguished from R. sumatranus by the size of the outer incisor, and by the conformation in many respects of nearly all the teeth, and especially of the premolars; but as we are now concerned only with the second upper molar, I will limit what I have to say to that tooth alone. As regards the dorsum (fig. 5, p. 414), the resemblance between this surface in R. sondaicus and in the Sarawak tooth is obvious at first sight; the only difference, so far as 1 can perceive, is in the circumstance that the anterior costa (a c) is not prolonged quite to the base of the crown ; but this, I think, may be explained by the immature condition of the Sarawak specimens. But by this surface alone it would not be easy, I conceive, or even possible, in some cases, to distinguish between R. sondaicus and R. sumatranus, as shown in figure 6 (p. 414), which represents the dorsal surface of the same tooth in R. sumatranus. The chief points upon which I should rely, as showing the identity of the Sarawak teeth with those of R. sondaicus, are:-1, the wide angle at which the crochet (c) is given off (fig. 7, p. 415) ; 2, the emargination and absence of a denticle on the posterior vallum ; 3, the comparatively greater transverse as compared with the longitudinal diameter of the crown,-since in R. sumatranus the crochet springs at a right angle or even less from the hinder column (fig. 8, p. 415), and the posterior vallum, which has a more or less crenate edge, presents a very distinct and constant * Under this name I include R. nasalis, B. stenorhynchus, and B. floweri of Dr. Gray, not because I would venture at present to decide as to the true relations of these forms to each other, but because the dental characters at any rate, so far as I can perceive, afford no sufficient distinctions between them ; and one thing appears abundantly clear, that, as contrasted with other well-marked species, they all constitute a group apart which I should myself regard as specific. |
