MACROPODID^E 167 



small or wanting. Upper incisors small, decreasing in size from first 

 to third. Fourth premolar small, hour-glass shaped, and without 

 inner ledge. Molars as in Macropus. 



This genus contains three species, having the same distribution 

 as Lagarchestes. Mr. 0. Thomas observes : " The spur-tailed Wallabies 

 form a natural little group, distinguished both by the shape of the 

 incisors and the peculiar horny excrescence at the tip of the tail. 

 The latter character is altogether unique among Marsupials, and is 

 only found among other mammals in the Lion, which occasionally 

 has a somewhat similar horny spur at the end of its tail. In the 

 case of the Wallabies it is difficult to conceive what can be the 

 use of this spur ; and observations on the living animal are much 

 needed with regard to this interesting point." 



Petrogale. 1 Muffle naked. Fur of nape directed backwards. 

 Claw of fourth hind digit very short. Tail long, cylindrical, thinner 

 than in Macropus, and thickly haired and pencilled at the extremity. 

 Skull as in the smaller species of Macropus, with large posterior 

 palatal vacuities, and the bullse sometimes inflated. No canine. 

 Upper incisors small, the third resembling that of Macropus. Fourth 

 premolar large and stout, as in some of the Wallabies, with a con- 

 tinuous inner ledge, and two or three indistinct vertical ridges 

 externally. Molars as in the Wallabies. 



This genus is represented by six species, of which P. penicillata 

 is a well-known example, ranging over the whole of the mainland of 

 Australia. The Rock- Wallabies, as its members may be called, are 

 very closely allied to some of the true Wallabies ; and some hesitation 

 may be expressed as to the advisability of accepting their generic 

 separation from Macropus. They inhabit rocky regions, making 

 their retreats in caverns and crevices, leaping with surprising agility 

 from one narrow ledge to another, and browsing upon the scanty 

 herbage that the neighbourhood of such situations affords. The 

 species are P. xanthopus, P. penicillata, P. lateralis, P. concinna, P. 

 brachyotis, P. inornata. 



Remains of P. penicillata are found in a fossil state in the 

 Pleistocene cave-deposits of New South Wales. 



Macropus? Muffle generally completely naked. Ears large. 

 Fur on nape (with an occasional exception in two species) directed 

 backwards. Claw of fourth hind digit very long. Tail thick, 

 tapering, and evenly furred. Four mammae. Skull (Fig. 55) long, 

 smooth, and rounded ; the nasals expanded behind ; generally large 

 palatal vacuities ; and the auditory bullae not inflated. Canine 

 minute, and shed at an early period. Incisor series forming an 

 open curve ; the first the tallest, and the third nearly always the 

 longest antero-posteriorly, and generally with an infolding of enamel 



1 Gray, CharleswortK s Mag. Nat. Hist. vol. i. p. 583 (1837). 

 2 Shaw, Naturalist's Miscellany, vol. i. pi. xxxiii. (1790). 



