114 
LOWER MAMMAL GALLERY. 
The Yapock or AVater- Opossum, Chironectes mimnms ( 1447 ),- 
ditfers from other Opossums in having its toes webbed like 
those of an Otter ; it is wholly aquatic in its habits, and lives 
on water-beetles and crustaceans. Its colour is of a general 
ashy grey, with five or six broad slaty-brown bands across the 
back, standing out in high relief against the ground-colour of 
the body. 
Fossil remains of Opossums are of special interest, on account 
of being found in the Eocene deposits of England and France. 
These fossils consist, however, chiefly of lower jaws, so that it 
is by no means easy to tell their exact relations to their modern 
representatives. 
The family Kotovyctidcv consists of a single species inhabiting 
the sandy deserts of the centre of Australia, the Marsupial 
Mole, Notoryctes typlilops ( 1443 ). This little animal bears very 
much the same relation in its structure and habits to the other 
Marsupials that the Moles and Golden Moles (pp. 31 & 33) do 
to the other Tnsectivora, and the Mole-Rats (p. 60) present to 
other Rodents. It lives chiefly underground, burrowing in the 
sandy soil, and feeding on worms, grubs, &c. Its snout is 
provided with a peculiar naked pad or shield with which it 
forces its way through the earth ; the tail is short and entirely 
naked ; the eyes are practically aborted, as also are the ears ; 
and the fore-feet, with which it burrows, are modified somewhat 
in the same way as are those of the Golden Moles {Chrysocliloris) . 
The third and fourth toes bear large digging claws, while those 
of the other three are small and slender. 
The skeleton of this little animal, exhibited in case 70, is 
remarkable for its generally Mole-like structure, powerful 
fore-limb, with its stout and highly ridged humerus, the united 
neck-vertebrae, the first and the seventh being alone free, and 
for the peculiar roofing-in of the sacrum by the expansion of 
the processes of the sacral vertebrae. The teeth vary slightly 
in number, but the ordinary formula appears to be : — I. f, 0. {, 
P. -b M. f = 40. 
A second South American group is now represented by the 
living genus Ccenolestes, referred to the family Epanorthidcv , of 
which numerous fossil remains have been discovered in the 
