87 



the surf crashes, and on the Hchen-covered boulders of the summit, nearly 

 800 feet above, where moss, ferns, and casuarinas of large growth constitute 

 a very distinct environment. 



It does not exist upon the southern portions of the main northern island, 

 and almost certainly it is absent from the southern detached portions of the 

 group. Its area even on the Pearson group is therefore a peculiarly restricted 

 one, and it is rather remarkable why it should be confined to only one of the 

 three partially connected masses which constitute the complex northern main 

 island. 



The wallaby has no obvious natural enemy ; the sea eagles, crows, and sea 

 lions may possibly take occasional toll of young or sick, but from its habit of 

 sitting exposed on a rock at any time of the day it would appear that there was 

 but little threat to its safety in the normal condition of its environment. In 

 November some females were seen with large young still in the pouch ; in 

 January and February the young are all running with the parents. 



Certain points of anatomical interest may be mentioned. In those lizards, 

 such as Amphibolurus, which lie basking in the most direct rays of the sun, 

 the viscera are shielded by membranes in which a black pigment is developed. 

 In particular the male genital gland is usually black above and yellowish-white 

 beneath, the surface uppermost in the basking position of the animal being pro- 

 tected by pigment. In Petrogale pcarsoni the male genital gland is completely 

 enveloped in a pigmented membrane, the tunica vaginalis being almost entirely 

 black. Like the lizards, the wallaby will sit in the hottest noon-tide sunshine, 

 and it appears to experience no discomfort when seated upon a granite boulder 

 so hot that a man could not stand, let alone sit, upon it for any considerable 

 time. The curiously padded feet, with the shortened claws, and lateral fringe 

 of hairs, are very perfect adaptations to the environment of granite boulders ; 

 a human being needs rubber soles in order to get about on Pearson Islands, 

 but no rubber sole can rival the rock wallaby's specialized foot (see fig. 7). 



It has been noted above that the rock wallaby does not use its tail in the 

 fashion of a typical "scrub" wallaby, and in accordance with this physiological 

 fact is the anatomical condition of the absence of any tail-pad, by which is 

 meant the thickening of the subcutaneous tissues, which marks the contact 

 point of the kangaroo's tail with the ground. The tail of Petrogale pearsoni 

 may be pulled out of the skin in the same way as that of a rat — the skin will 

 slip off the underlying tissues because there is no tail-pad. But the tail of a 

 kangaroo or "scrub" wallaby cannot be treated in this fashion, for the tail-pad 

 forms a bond between skin, subcutaneous tissue, muscle, and tendon. 



Although the existence of this wallaby has been long known, it is a remark- 

 able thing that no specimens seem to have ever been examined and compared 

 with other, continental, rock wallabies. Since no satisfactory series was available 

 for an adequate study of its nearest allies, a skin and skull were sent to Mr. 

 Oldfield Thomas, and by him the animal was .diagnosed as a new species and 

 described under the name of Petrogale pearsoni (Ann. and Mag. Nat. Hist., 

 Ser. 9, vol. ix., p. 681, 1922). It is most nearly related to P. lateralis, the 

 Western Australian rock wallaby of the Swan River district, and to P. hacketti, 

 of Mondrain Island. It is therefore a very far eastern outlier of its group. 

 The description of the type specimen is as follows: — "Size comparatively small, 

 about as in lateralis, decidedly smaller than in hacketti. General colour, on the 

 whole, very much as in lateralis, paler than in hacketti. Dark lateral lines of 

 the underside, however, more blackish, those of lateralis being dark brown. 

 White patches at the base of the ears larger and more prominent. Tail with 

 its upper- and undersurfaces, from about 3 inches from the base, contrasted 

 black, the sides dull bulTy-whitish ; above, the black soon fades off into 



