MACROPODIDA 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 Lagorchestes. Mr. O. 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._— 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 bulle 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 Jfacropus. 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.2—Muffie generally completely naked. Lars 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 mamme. Skull (Fig. 55) long, 
smooth, and rounded ; the nasals expanded behind ; generally large 
palatal vacuities; and the auditory bulle not inflated. Canine 
minute, and shed at an early period. JIncisor 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, Charlesworth’s Mag. Nat. Hist. vol. i. p. 583 (1837). 
2 Shaw, Naturalist’s Miscellany, vol. i. pl. xxxiii. (1790). 
