266 
Leyden Museum, the canines have a longitu- 
dinal groove on the outer side. 
The characteristic form of the trenchant pre- 
molar has just been alluded to: its maximum 
of development is attained in the arboreal Po- 
toroos of New Guinea ( Hypsiprymnus ursinus 
and Hyps. dorcocephalus ), in the latter of which 
its antero-posterior extent nearly equals that 
of the three succeeding molar teeth. In all the 
Potoroos the trenchant spurious molar is sculp- 
tured, especially on the outer side, and in 
oung teeth, by many small vertical grooves. 
e true molars each present four three-sided 
pyramidal cusps; but the internal angles of 
the two opposite cusps are continued into each 
other across the tooth, forming two angular or 
concave transverse ridges. In the old animal 
these cusps and ridges disappear, and the grind- 
ing surface is worn quite flat, as in fig. 91, 
which represents the dentition of the original 
Potoroo, described in White’s Voyage. 
Genus MACROPUS. Kangaroos. 
In the genus Macropus (fig. 92) the normal 
condition of the permanent teeth may be ex- 
pressed as follows :-— 
P 3—3 ss o0—oO 
Incisors, — 3 canines, poe. ; premo- 
lars, emake ; molars, ee. a8, 
1—1 4—4 
The main difference, as compared with Hyp- 
siprymnus, lies in the absence of the upper 
canines as functional teeth; the germs, how- 
ever, of these teeth are always to be found in 
the young mammary fcetus of the Macropus 
major, and I have seen them a but of 
very small size, and concealed by the gum, in 
the adults of some small species of kangaroos, 
Macropus major, one-third nat. size. 
as Macropus rufiventer, Ogilby, and Macr. 
psilopus, Gould. This, however, is a rare ex- 
ception ; while the constant presence and con- 
spicuous size of the canines will always serve to 
istinguish the Potoroo from the Kangaroo. 
But ‘there are also other differences in the form 
and proportions of certain teeth. The upper 
incisors of the Macropi have their cutting 
margins in the same line, the anterior ones not 
being produced beyond thatline, as in the Hyp- 
siprymni: the third or external incisor is also 
broader in the kangaroos, and is grooved and 
complicated by one or two folds of the enamel, 
continued from the outer side of the tooth ob- 
MARSUPIALIA. 
liquely forward and inward. Tn most 
the anterior fold is re ted by a 
groove: the relative size of the outer 
the extent and position of the i 
enamel, and consequently the proportions | 
the part of the tooth in front or behind it, va 
more or less in every species of Macrom 
there are two folds of enamel near the ante 
part of the tooth in Macr. major, and 
terior portion is of the greatest extent, ai 
entire crown of the tooth is relatively br 
in this species. The middle incisor is 
also complicated by a posterior notch 
an external groove. ese modifications of 
external incisors of the kangaroos were first 
ticed by Mr. Jourdan, and subgeneric disti 
tions, with names often sufficiently unmean 
if not absurd,* have been subsequently b 
upon them; but such dental characters pos 
neither sufficient constancy nor physiole 
eae to justify such an application. 
. Fr. Cuvier has propel a binary 
sion of the genus Macropus, as here defit 
founded on the absence of permanent 
molars, and a supposed difference in the” 
of succession of the true molars in certair 
cies of Kangaroo, combined with modifical 
of the muzzle or upper lip, and of the tail. 
The dental formula which I have ass 
to the genus Macropus is restricted in its 
plication by that naturalist to some small; 
cies of Kangaroo, grouped together under 
term Halmaturus, originally applied by I 
to the Kangaroos generally.+ The rest 
Kangaroos, under the generic tem M 
pus, are characterised by the following « 
molars, — 
The truth, however, is 
both the Halmaturi | 
Macropi of M. Fr. Cu 
have their teeth deve 
in precisely the same 
ber and manner: they 
differ in the length of 
during which certain of 
teeth are retained.{ I 
great Kangaroo, 
ple, the permanent pret 
which suceeeds the e 
ponding deciduous or 
the vertical direction, 
pushed out of place 
shed by the time the 
Sern 
ex 
formula :—lIncisors, = 
* E.g. ia, Gray, Petrogale, Gray, 
signifies ‘ rock weasel.’ 
t Prodromus Systematis Mammalium et . 
8vo. 1811. The dental character which 
cellent naturalist gives, accurately expi 
condition of the canine or laniary teeth, * 
niarii aut nulli, aut superiores 2 ambigui, 
in medio inter primores et molares ce 
80; but there are never more than five mola 
place on each side of each jaw in the Kangar 
¢ M. Fr. Cuvier was aware that a deciduous” 
rious molar existed in the great indo} 
species of his subgenus Macropus, but he belli 
that it was peculiar to an early period of life, 
then existed only in a rudimental state 
ee 
— as 
germeé,” and that instead of being disp 
