338 ROBERT COLLETT, 



they are strongly curved outwards to the sides, so that the greatest 

 breadtb between the crests (straight across the hind margin of the 

 temporal proc. zygomaticus) is but inconsiderably less thao the great- 

 est height of the skull. Towards the back the crests again converge 

 a little. 



The OS interparietale is comparatively broad (length 10 mm, 

 breadth 4| mm), and with the lateral angles obtuse. The buUae 

 osseae are large and strongly inflated ; their greatest length (which 

 in A is 8 mm, in B 8,8 mm), is about equal to the length of the 

 orbital margin from the nasalia to the front angle of the parietale 

 (9 mm). They are thus contained in the length of the skull 4,25 and 

 4,02 times. 



The nasalia are somewhat depressed along the middle; they are 

 of medium length, and extend to just above the root of the incisors. 

 The foramina incisiva are very long and reach to the centre, or to a 

 point just behind the centre of m ^. 



The dentition in both specimens is : » | m f (16). 



The molars have the tubercles a little worn, but these appear 

 to present exactly the same pattern, as in M. rattus, although they 

 are considerably stronger and broader. 



Length of dental series : upper jaw 7 mm, lower jaw 6,8 mm. 



3. Mus assimilis Gould 1857. 

 Ml/s assimilis Gould, Proc, Zool. Soc. Lond. 1857, p. 241 (1857). 



A. Coomooboolaroo, Dec. 1883 (skin with skull). 



In colour M. assimilis on the whole closely resembles the pre- 

 ceding species, but it is not quite so reddish in hue ; the für appears 

 to be softer and longer, and the back is supplied with long black 

 interspersed hairs. 



The length of the body in the Single specimen is about 165 mm, 

 the tail 115 mm. The number of rings on the tail is 128. 



The skull. Length of skull 43 mm, breadth 21 mm. 



The skull differs from that of the preceding species especially in 

 its more elongated shape, and in its very small buUae osseae, as well 

 as in the structure of the teeth. 



