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Show 1876.] DENTAL CHARACTERS OF RHINOCEROSES. 453 the most specialized of all the living Rhinoceroses. The broad form of the front of the lower jaw, as compared with R. bicornis, is quite well seen in these very young specimens. With regard to the molar teeth, the same kind of difference occurs between these forms as between the two Indian one-horned species. The larger one has a greater complexity of arrangement, derived from the more frequent union of crochet and crista, cutting off an accessory valley. But it must be noticed that there is an extraordinary variation iu this respect between two examples of R. simus of nearly the same age in the British Museum, so great, indeed, that, if supported by other characters, they might be taken to indicate specific distinctness. In fact they either do this or show that the precise pattern of the enamel-folds of the molar teeth, so much relied upon by palaeontologists to distinguish species, is a rather uncertain character. In one of these skulls (No. 1003a) the crochet and crista are united in all the premolar and molar teeth of both sides. In the other (No. 1003 b), an older specimen, and somewhat smaller, though presenting all the general characters of the species, they are united only in the left second premolar, in both third premolars, in both first molars and in the right third molar. The want of symmetry throws some doubt upon the value of this character*; otherwise it might, combined with the smaller size and narrower nasals of this specimen (perhaps only sexual differences?), lend some countenance to the common belief among African sportsmen and travellers, that there is a second large species allied to R. simus. In the smaller African rhinoceros, R. bicornis, the crochet and crista of the molar teeth are both well developed, but rarely united in the true molars, though frequently so in the premolars. Whether there is one or more species of this form, has long been debated by zoologists ; but those who have given their verdict for two have founded their decision solely on external characters, chiefly the form and size of the posterior horn, and no attempt has ever been made to show whether any osteological or dental characters were correlated with these. In fact, until very recently there were no materials accessible for the investigation. The acquisition by the British Museum of two complete skeletons of the reputed R. keitloa, and others of R. bicornis, with the horns attached, has, however, rendered the investigation a practicable one. I have not yet had the leisure to make the careful examination of the whole skeleton which would be desirable ; but, comparing the skulls and teeth of perfectly adult individuals presenting both varieties of horns, I have not been able to detect any differences either of size, general proportions, or relations of the various bones to each other, that could reasonably be called specific. All that can be inferred from this is, that I have not at present seen any thing derived from osteological or dental structures to confirm the belief in the existence of more than one species of the smaller type of African rhinoceros. Other observers may, with more ample materials, be more fortunate ; and I * And its variability as before noted, in specimens of undoubted R. unicornis. |