420 T\rr. 0. Thomas on 



corresponding tooth is also conspicuously broader and 

 heavier in llacl-etti than in true lateralis. 



I think it probable that P. I. Racketti is not a true insular 

 form, but that it will be found to occur in suitable localities 

 on the mainland of S.E. West Australia, diminishing in size 

 and strength of dentition northwards. 



In accordance with a suggestion of Mr. B. H. AYoodward's, 

 I have named this handsome rock-wallaby in honour of 

 Dr. Ilackett, Chairman of the Western Australian Museum 

 ConiUiittee. 



Thalacomys^ sagitta, sp. n. 



In the Catalogue of Marsupials all the specimens of 

 Thakicomys — there called Peragale — were referred to a single 

 species, 2h. lagotis^ without distinction between the West- 

 Australian and South-Australian examples. But. the recent 

 presentation of a fine specimen from South Australia by 

 Mr. Hillier has drawn my attention to the fact that the form 

 found in that district is so considerably smaller than the West- 

 Australian one that the two ought certainly to be separated. 

 The difference is mainly in the skulls, and may be readily 

 appreciated by comparing the measurements given below of 

 the South-Australian animal with those of the typical West- 

 Australian form published in the Catalogue. 



Externally, apart from the corresponding difference in 

 size, there is little to distinguish the two forms. On the 

 whole Th. sagitta is a little paler in tone, the black band on 

 the tail is slightly shorter, being shorter instead of longer 

 than the white end, and the feet are paler below, the black 

 only extending about a third of their length underneath the 

 heel. 



Dimensions in the flesh (measured by Mr. Hillier) : — 



Head and body 316 mm. ; tail 215 ; hind foot 91 ; ear 79. 



Skull: greatest length 85; basal length 76*5; greatest 

 breadth 38 ; nasals, length 40, greatest breadth 7"5 ; inter- 

 temporal breadth 13 ; palate length 50 ; basicranial axis 22*5 ; 

 basifacial axis 54; front of canine to back of last molar 36; 

 combined length of three anterior molariform teeth 12*5. 



Hah. South Australia. Type from Killalpanima, east of 

 Lake Eyre. 



Type. Adult male. B.M. no. 3. 5. 21. 2. Collected 6th 

 April, 1903, and presented by 11. J. Hillier, Esq. 



* Cf. Auu. & Mag. Nal. Hist. (7) v. p. I'l'o (1900). 



