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Show 1889.] MR. O. THOMAS ON A N E W GENUS OF MURIDAE. 247 black eyes. Mr. Fisk said there are also three white specimens of this animal in the Capetown Museum. A letter was read from Dr. E. C. Stirling, of Adelaide, containing a copy of his description of a new Australian Mammal (which had already appeared in nearly the same form in ' Nature,' vol. xxxviii. p. 583), as read before the Royal Society of South Australia, Sept. 4th, 1888, and published in that Society's 'Transactions.' Dr. Stirling was now engaged in finishing a complete description of this very peculiar and interesting burrowing animal, which somewhat resembled a Cape Mole (Chrysochloris) in general external appearance, and expected to be able to communicate it to this Society when ready. Mr. Seebohm exhibited the skin of a male example of Phasianus chrysomelas which had been purchased in the flesh (along with a female) in Leadenhall Market, where several others were also sold, and was stated to have been sent over in a frozen state from the Trans-Caspian provinces of Russia. The following papers were read:- 1. Description of a new Genus of Muridse allied to Hydromys. B y O L D F I E L D THOMAS.. Natural History Museum. [Eeceived March 26, 1889.] (Plate XXIX.) One of the most singular and at the same time most isolated genera of Muridae is Hydromys, of which the only species is the well-known Australian Water-rat. Alone of the family, and, with one exception **, alone of the Rodentia, this remarkable animal has only two molars on each side of each jaw, and the structure of these molars is at the same time quite different from that found in any other known Rat. Externally Hydromys has taken on characters suitable for a purely aquatic life, standing, so far as regards external specialization for swimming, in an intermediate position between Potamoyale and Nectomys2, less specialized than the former and more so than the 1-itter. The skull of Hydromys differs from other Muridae in many characters, and especially in the structure of the infraorbital foramen, which is hardly murine in the ordinary sense at all, as it is of about the same breadth above and below, and its external wall has not the anteriorly projecting plate found in the great majority of the Rats and Mice (see Plate X X I X . fig. 7). Altogether Hydromys has occupied a peculiarly isolated position in the family, no other genus showing any approach towards it, and there is therefore a proportionate amount of interest in the discovery of a new form allied to it. The proof of alliance lies wholly in the 1 Heterocephalus phillipsi, see P. Z. S. 1885, p. 847. 2 Peters, Abb. Ak. Berl. 1860, p. 152. Regarded as a subgenus of Holochilus, Thomas, P. Z. S. 1882, p. 101. 17* |