on Australasian Eats. 429 



Skull : greatest length 37-5 ; condylo-incisive length 35*5 ; 

 zygomatic breadth IS'S ; nasals, length 13-7, breadth at half 

 their length 38; interorbital breadth 5'2 ; breadth o£ brain- 

 case 16-3; palatilar length 16-8 ; palatal foramina 7'2x2'2j 

 upper molar series G. 



Hah. Mondrain Island, off Esperance, south coast of 

 Western Australia. 



7'i/pe. Old male. B.M. no. 7. 7. 18. 3. Collected 29th 

 April, 1906, by J. T. Tunuey. Presented by the Western 

 Australian Museum, Perth. Two specimens. 



This island rat is alone related to ll.fuscipes, a species 

 which, in spite of various references from other parts of the 

 continent, I believe to be strictly confined to Western 

 Australia. The new form, while very similar externally, 

 may be readily distinguished by the cranial details above 

 described. 



This species and the true R. greyi of S. Australia are 

 exceptions to the statement made by me"^ that all Australian 

 members of Raltas have supraorbital ridges; but it is quite 

 evident that they really are liattus, and not Fseudomys. 



Ilydromys iiauticus, sp. n. 



Size rather small, about as in H. heccarii. General colour 

 above dark greyish brown, near " hair-brown," the middle 

 dorsal area more blackish, quite black on the forehead, crown, 

 and nape. Sides greyer. Under surface drabby, the hairs 

 pale slaty at base, with ''pinkish bufi"' ends. Hands pale 

 brownish. Feet almost naked, their fine hairs dull whitish. 

 Tail, as usual in the northern forms of the genus, with nearly 

 half of the short-haired portion white. 



Skull about as in H. heccarii, with similarly broad heavy 

 muzzle. Incisors very pale yellow in front. Molars rather 

 small. 



Dimensions of the type (measured in flesh) : — 



Head and body 2G5 mm.; tail 215, its white terminal 

 portion 79 ; hind foot 50 ; ear 22. 



Skull : greatest length 55 ; condylo-incisive length 52*5 ; 

 zygomatic breadth 27 ; breadth of muzzle on premaxillo- 

 maxillary suture 10'8; nasals 17 X 6*6; intertemporal breadth 

 G"8 ; breadth of brain-case 20 ; palatilar length 25 ; palatal 

 foramina 6'lx3*7 ; upper molars 8*1 ; breadth of di} 2''6. 



Hah. Aru Islands ; type from Dobo. 



Type. Old female with worn teeth. B.M. no. 10. 3. 2. 14. 

 Original number 758. Collected 8th April, 1909, by W. 

 Stalker; presented by the New Guinea Ex[jedition. 

 * Ann. & Mug-. Nat. Hist. (8) vi. p. 604 (1010). 



