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Show 456 ON THE CRANIAL CHARACTERS O F R H I N O C E R O S E S . [May 16* b. Larger size. Incisor teeth, if ever present, disappearing very soon after birth. Molar teeth with crista and crochet generally united. Front end of mandible depressed and spatulate. 2. A. SIMUS, Burchell (Bull. Soc. Philomat. p. 96, 1817). A. oswellii, Gray (P. Z. S. 1853, p. 46). In reference to the name of this group, Ccelodonta (Bronn, Jahrbuch fiir Mineralogie, 1831, p. 51) was proposed for some teeth supposed to belong to a new genus allied to Rhinoceros, but subsequently identified as those of the well-known R. tichorhinus, Cuv.* It can scarcely be retained, however, for the group now under consideration, as its definition would include R. unicornis, and exclude many of the species without incisor teeth. It was, in fact, never equivalent to Pomel's Atelodus, though it might be used (as by Dr. Gray, loc. cit. 1867) by any one who thinks fit to separate R. tichorhinus generically from all the other members of the family. In the Catalogue of the bones of Mammalia in the British Museum (1862), Dr. Gray uses Rhinaster for all the species of existing African rhinoceroses ; but in the memoir so often referred to above (1867) this name is limited to R. bicornis and R. keitloa, and Ceratotherium is introduced for R. simus. Rhinaster, as applied to the Rhinocerotidse, appears to be later than Atelodus. It was, moreover, proposed by Wagler (Syst. Amphib. 1830) as a substitute for Uliger's genus Condylura (Insectivora), on account of the latter being inappropriate; but it has not been generally adopted. As the termination of such a term as Ceratotherium, by common consent of zoologists, has hitherto been restricted to extinct genera, its application to B simus is inconvenient. Fortunately, in the grouping proposed above, the name is unnecessary, as the members of the family with the incisor teeth small or absent form a well-characterized, even if somewhat artificial, generic group, which scarcely needs further subdivision. Although most of the known extinct species of Bhinoceros may be arranged under one or the other of the above sections, the definitions would have, as, indeed, might be expected, to be considerably modified to include them. Thus B. schleiermacheri, Kaup, of the late European Miocenes, though allied to B. sumatrensis in possessing incisor teeth and two horns, and so far coming under the definition of Ceratorhinns, retains the central lower incisors of Bhinoceros proper, and has the post-glenoid and post-tympanic processes united, as, indeed, have all the extinct forms that I have examined. On the supposition that this species is the direct ancestor or representative of the Ceratorhinns group of modern times, the presence of the four inferior incisors, as a more generalized character, is quite natural ; but the structure of the squamosal is not so easy to understand, as being more specialized than in the modern species. Precisely the same occurs with the former representatives of the Atelodus group, of * R. antiquitatis, Blum., is the earliest name for this species, and is adopted by Brandt and Dr. Falconer, though Cuvier's name still holds its ground with most authors. |