sovie Australasian Mammals. 425 



Petrogale lateralis Ilachetti^ subsp. ii. 



Closely similar to true P. lateralis in external and cranial 

 characters, including both colour and pattern o£ markings, 

 but larger and with larger teeth, especially with larger 

 anterior premolar or "secator''^* [p^ of the Catalogue of 

 Marsupials). 



Dimensions of the type (measured in skin) : — 



Head and body 660 mm. ; tail 540 ; hind foot (s. u.) 139 ; 

 ear 55. 



Skull: greatest length 107; basal length 93; greatest 

 breadth 50 ; front of orbit to back of skull 62 ; nasals, 

 length 47, greatest breadth 14-3 ; interorbital breadth 18'3 ; 

 diastema 20; palatal foramen 8; large secant premolar 8'3 

 x4'l; combined length of three anterior raolariforin 

 teeth 18-5. 



Hah. Mondrain Island, off the coast of S.E. Western 

 Australia. 



Type. Adult male. B.M. no. 5. 4. 1. 5. Original 

 number 7161. Collected 1st November, 1904, by J. T. 

 Tunney. Presented by the Western Australian Museum, 

 Perth. Fourteen specimens examined. 



While in colour and other external characters I can find 

 no difference between the Mondrain-Island rock-wallabies and 

 the typical specimens of P. lateralis described and figured by 

 Gould, there is so marked a distinction in the size of the 

 skulls and teeth, especially of the large secant premolar, that 

 it is clear that the former cannot be referred to Gould's 

 animal. 



Among five skulls of P. lateralis none exceed 95 mm. in 

 total length, the front of the orbit about 5o mm. from the 

 back of tlie skull, and the upper secator 6"8 mm. in length 

 by 3'1 mm. in breadth, the tooth markedly narrowing 

 forwards, while in Hachetti it is a long and comparatively 

 broad oval, nearly as broad in front as behind. Below, the 



* This tootli, the most important for systematic work in the Marsupials, 

 might conveniently be called the "secator," thus avoiding altogether the 

 confusing question of its serial homology. It is the "p"' of the Cata- 

 logue of Marsupials, but is now more usually believed to be homologous 

 with p^ or, more probably, mi>^, of Placental mammals. This change of 

 opinion, even if it were accepted universally — and the question is still 

 imder discussion, — renders the use of a numerical symbol exceedingly 

 inconvenient for ordinary systematic descriptions ; and it is hoped that a 

 special name for the tooth will be of as much value to workers on 

 marsupials as ''carnussial " has proved to writers on Carnivora. 



