18/6.] DENTAL CHARACTERS OF RHINOCEROSES. 449 



similar conformation, subject to individual variation. This never 

 takes place in the true molars of R. sondaicus (though it may 

 occasionally in some of the milk-molars, especially the second), as in 

 fact the crista is rarely developed in that species, and the crochet is a 

 simple straight free process in the true molars, though often double 

 in the premolars. 



On the other hand the molar teeth of R. sondaicus and R. 

 sumatrensis are remarkably alike. Mr. Busk, it is true, has pointed 

 out characters by which they can be distinguished* ; but they are 

 such as to require great attention on the part of the observer to 

 detect, and one of them, the difference in the relative length and 

 breadth, does not appear to me to bear the test of application to a 

 considerable series of individuals. I may, however, add another, 

 which appears to be tolerably constant, viz. the greater depth of the 

 posterior as compared with the median sinus in R. sumatrensis, 

 whence it results that in an extremely worn tooth of the latter 

 there are always two fossae, the median and posterior, while in R. 

 sondaicus the posterior disappears, leaving finally only a single fossa 

 in the wide surface of exposed dentine. In R. unicornis, in a cor- 

 responding stage of attrition, there are three fossa; — the median, 

 accessory, and posterior. 



The premolars of R. sumatrensis can be distinguished from those 

 of R. sondaicus by the complete absence of the double crochet 

 above mentioned as usually, if not always, present in the latter. 



It is a curious circumstance that the remains of R. sondaicus, 

 though more recently distinguished as a distinct species, are more 

 abundant in our collections than those of R. unicornis. In the Col- 

 lege-of-Surgeons Museum there are 9 skulls of this species, and 

 5 of R. unicornis. In the British Museum the numbers are 

 respectively 9 and 7. This may be accounted for by the geogra- 

 phical range of the species, as it is R. sondaicus which inhabits the 

 Bengal Sunderbunds, and the neighbourhood of Calcutta, while R. 

 unicornis is only known from the hilly country to the north, bordering 

 upon Nepal, Bhotan, and Assam. On the other hand, judging from 

 the figures, nearly all the living examples of rhinoceroses brought 

 to this country before the present specimen of R. sondaicus, which 

 was acquired by the Society in 187-1, have belonged to the species 

 which we call R. unicornis ; but this is a subject which has been 

 discussed in Mr. Sclater's article on the species of Rhinoceros 

 living in the Society's Gardens, shortly to be published in our ' Trans- 

 actions ' with magnificent illustrations of external characters of five 

 species drawn from life. 



To return to the collection of skulls. Judged by the tests above 

 given, and by other characters more difficult to desciibe, but easily 

 appreciated on an examination of the specimens, the one described 



of the Discovery at Sarawak, in Borneo, of the fossilized Teeth of Bhinoceros." 

 In one of the specimens of R. unicornis in the British Museum, though the 

 crochet and crista are well developed, there is no actual union of their extremities. 

 * Loo. cit. 



