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Show 364 DR. C I. FORSVTH MAJOR ON THE [Mar. 16, account of its being the only Ungulate of the recent Malagasy fauna and closely related to the species of an African genus; whilst all the other Mammals, with the exception of the Chiroptera, a Crocldura, and the Vlverrlcula, belong to distinct genera. Por this reason it has been supposed by Blanford that the genus Potamochcerus did not exist in Africa when Madagascar was connected with that continent, but found its way there at a later time (at the end of the Pliocene or later Pleistocene), when the connection with Africa was severed, so as to prevent most of the present African Mammalia from crossing over ; wdiilst Potamochcerus, being a good swimmer, might have been able to cross the Strait. This hypothesis reposes, of course, on two assumptions: first, that the Strait of Mozambique was very much narrower in later Pliocene times than at present; and secondly, on its being taken for granted that the Malagasy Potamochcerus is different from all its African congeners. Eor it is obvious that if the Malagasy Wild Hog is specifically identical with one of the continental species, it must have arrived in the island at a very recent date ; and in that case, the most likely supposition would be that for some reason or other it had been carried over by man, as must be supposed to have been the case with regard to Vlverrlcula malaccensis. The question as to the specific distinctness is not in the least settled at present. There has been in the Natural History Museum, for some months, a mounted specimen of a Potamochcerus from Nyasaland, which in colour and general outer appearance so closely resembles the Malagasy form that very few zoologists would venture to separate them on account of some slight differences in the respective skins. On the other hand, most of the cranial characters mentioned as distinctive between the Malagasy form and the P. chceropotamusl are of such little value, being very variable, that no importance can be attached to them. Such are: the position of the mental foramina in the lower jaw, the more or less irregularity it the lower contour of the zygomatic arch, and the conformation cf the lateral depression in the region of the lachrymal and the upper part of the maxillary. U p to the present time, besides the skin of a very young specimen, only one skull of the Malagasy form, that of an adult male, existed in the Natural History Museum. I have brought back from the Upper Eorest Region of the island the remains of eight specimens, viz. six skins with their skulls complete, besides a complete skeleton and a separate skull, making in all eight skulls of different ages and both sexes. Twro of the skulls, a male (see figs. 1 and 2, p. 365) and a female (Pl. X X V . fig. 2 and Pl. X X V I . fig. 2), are now exhibited. As a result of m y comparisons I have to state that there are very constant cranial characters which enable us to distinguish the Madagascar form from the P. chceropotamus, with which, on the whole, it has more affinities than with the West-African P. porcus. 1 J. E. GRAY. " On the Madagascar River-hog {Potamochcerus) and on the Skulls of tbe three Species of the Genu- " (Ann. & Mag. N. H. xv. 1875, p. 45). |