224 LLOYD'S NATURAL HISTORY, 
PART II. 
MONOTREMES--ORDER MONOTREMATA. 
INTRODUCTION. 
At the commencement of the first part of this work it was 
shown that the Marsupials, or Pouched Mammals, constitute 
not only a distinct order (Marsupialia) in the Mammalian class, 
but that they likewise form a separate sub-class variously known 
as the Didelphia, Metatheria, or Impilacentalia, in opposition 
to the group known as the Monodclphia, Eutheria, or Placen- ; 
talia, which contains all the other members of the class save 
those to be now considered. 
The representatives of this latter group, which are very few 
in number, and strictly confined to Australia, Tasmania, and 
New Guinea, are known as Monotremes, or Egg-laying Mam- ; 
mals, and agree with the Marsupials in constituting not onlya 4 
distinct order (Monotremata), but likewise a separate sub-class; | 
—the sub-class being designated by the name of Ornithodelphia, 
or Prototheria. So vast indeed is the difference between these 
Ege-laying Mammals and all other members of the class to 3 
which they belong, and so closely do they connect the latter 
with the lower classes of the Vertebrate sub-kingdom, that some . 
systematic zoologists do not consider that their separation as a 
sub-class of equivalent rank with those respectively containing 4 
the Pouched and the Placental Mammals, sufficiently emphasizes ; 
= 
