1889.] MB. O. THOMAS OxV A NEW GENUS OF MURID^. 247 



black eyes. Mr. Fisk said tliere 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 {Chrysocldoris) 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 purcliased 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 Muridge allied to Hydrvmys. 

 By Oldfield Thomas, Natural History Museum. 



[Eeceived March 2(), 1889.] 



(Plate XXIX.) 



One of the most singular and at the same time most isolated genera 

 of Muridae is Hydromys, of which the otdy 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 Potamogale and Nec- 

 tomys^, less specialized than the former and more so than tlie Intter. 



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 XXIX. 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 



^ Hetcrocepkalus phiUipsi, see P. Z. S. 1885, p. 847. 



- Peters, Abh. Ak. Berl. 18(50, p. 152. Eegavded as a subgenus of Holochihis, 

 Thomas, P.Z. S. 1882, p. 101. 



17* 



