Ee 
MARSUPIALIA. 
the preceding Bandicoots the canines are long 
and well i but the true molars have 
the grinding surface worn down flat in the full- 
grown specimens which I have, had the oppor- 
tunity of examining. 
The marsupial pouch in the Bandicoots, at 
least in the falbipeoten females of Per. nasuta, 
Per. obesula, and Per. Lagotis, has its orifice 
directed downwards or towards the cloaca, con- 
trariwise to its ordinary disposition in the 
Marsupials ; this direction of the pouch evi- 
dently relates to the procumbent position of 
the trunk when supported on the short fore 
and long hind legs. In the stomach and in- 
testines of a Perameles obesula I found only 
the remains of insects; and in the examination 
of the alimentary canal of a Per. nasuta, Dr. 
Grant obtained the same results. Nevertheless 
the Perumeles Lagotis, lately living at the Zoo- 
logical Gardens, refused meat and meal-worms, 
and subsisted on vegetable food exclusively. 
Genus CHG@ROPUS. 
_ The singular animal on which Mr. Ogilby 
has founded this genus, is briefly noticed and 
figured in Major Mitchell’s Australia, (Vol. ii. 
pl. 38, p. 131,) and the individual described 
is preserved in the Colonial Museum, at Syd- 
ney, N.S. Wales, (No. 35 of Mr. Geo. Ben- 
nett’s Catalogue.) 
It would appear that the two outer toes of 
the fore foot, which are always very small in 
the true Bandicoots, are entirely deficient in 
the Cheropus, unless some rudiments should 
exist beneath the skin ; at all events only two 
toes are apparent externally; but they are so 
developed and armed as to be serviceable for 
burrowing or progression. The inner toe is 
wanting on the hind-foot. Dental formula : 
1—1 
1—1’ 
—4. = 46. 
 Incisors, 
3s— 
. 
3 > 
= 3 canines, pre- 
—3 
molars, molars, 
’ All the teeth are of small size; the canines 
resemble the spurious molars in size and shape, 
and these are separated by intervals, as in Myr- 
mecobius. The marsupium opens downwards 
in the Cheropus, asin the true Bandicoots. The 
species described has no tail. The genus 
_ would seem by its dentition to rank between 
Myrmecobius and Perameles. Its digital cha- 
_ Yacters are anomalous and unique among the 
Marsupialia, but are evidently a degeneration 
from the Saltatorial or Bandicoot type. 
y. Scansoria. 
Genus DIDELPHYS, (Opossums, fig. 85.) 
These Marsupials are now exclusively con- 
fined to the American Continents, although 
the fossil remains of a small species attest their 
former existence in Europe contemporaheously 
_ with the Paleothere, Anoplothere, and other 
extinct Pachyderms, whose fossil remains cha- 
racterize the Eocene strata of the Paris Basin. 
The dental formula of the Genus Didelphys is,— 
5—5 —1 
oe, Ser ae oad 
7 3 1 
Incisors, canines, 
4 
<=: = 50. 
molars, ab 3; molars, 
3—3 
The Opossums resemble in their dentition the 
261 
Didelphys Virginiana. 
Bandicoots more than the Dasyures: but they 
closely resemble the latter in the tuberculous 
structure of the molars. The two middle in- 
cisors of the upper jaw are more produced than 
the others, from which they are also separated 
by a short interspace. The canines are well de- 
veloped ; the upper being always stronger than 
the lower. The false molars are simply conical, 
but are more compressed than in the Carnivo- 
rous Marsupials. The posterior false molar 
is the largest in the upper jaw ; the middle one 
is the largest in the lower jaw; the anterior 
one is the smallest in both jaws. The true 
molars are beset with sharp cusps which wear 
down into tubercles as the animal advances in 
age. The crowns of the upper molars present 
a triangular horizontal section: the base of the 
triangle is turned forward in the posterior mo- 
lar ; and obliquely inwards and outwards in 
the rest. In the lower jaw the true molars are 
narrower and of more equal size than in the 
upper jaw: there are five tubercles on each, 
four placed in two transverse pairs, the anterior 
being the highest, and a fifth forming the 
anterior and internal angle of the tooth: the 
anterior and external angle seems as if it were 
vertically cut off. 
The smaller species of Didelphis, which are 
the most numerous, fulfil in South America 
the office of the insectivorous Shrews of the 
old Continent. Their external resemblance is 
so close that some have been described as spe- 
cies of Sorex, but no true representative of 
this placental genus has hitherto been disco- 
vered in South America. The larger Opossums 
resemble in their habits, as in their dentition, 
the Carnivorous Dasyures, and prey upon the 
smaller quadrupeds and birds, but they have 
a more omnivorous diet, feeding on reptiles 
and insects and even fruit. One large species, 
(Did. cancrivora) prowls about the sea- 
shore and lives, as its name implies, on crabs 
and other crustaceous animals. Another spe- 
cies, the Yapock, frequents the fresh waters, 
and preys almost exclusively on fish. It has 
all the habits of an Otter ; and, in consequence 
of the modifications of its feet, forms the type 
of the sub-genus Cheironectes, Ill. Besides 
being web-footed the anterior extremities pre- 
sent an unusual development of the pisiform 
bone, which supports a fold of the skin, like 
a sixth digit; it has indeed been described, as 
such, by M. Temminck : this process has not, of 
course, any nail. The dentition of the Yapock 
resembles that of the ordinary Didelphis. All 
the Opossums have the inner digit of the hind 
foot converted by its position and development 
