DIDELPHYS. 195 
Subclass II. DIDELPHIA. 
Order IX. MARSUPIALIA. 
The great group of Marsupials, separated by most modern zoologists as a distinct 
subclass of the Mammalia, was widely spread over the globe in geological times ; 
but is now, as is well known, confined to the Australian and Neotropical regions. It is 
true that one species ranges far into North America; but the order, in the western 
hemisphere, is essentially characteristic of the Neotropical fauna, and is well represented 
in our subregion by both the known genera of the only New-World family, Didel- 
phide, which differs in several points from all the Australian forms *. 
Fam, I, DIDELPHIDZ. 
1. DIDELPHYS. 
Didelphis, Linnzeus, Syst. Nat. i. p. 71 (1766). 
Didelphys, Schreber, Saugth. ii. p. 532 (1778). 
Of the two forms of the family Didelphide which are well ascertained, the typical 
. genus Didelphys is suited for an arboreal, not an aquatic life, and is at once recognizable 
by its hind feet, the toes of which are not united bya web. It presents a large number 
of species, often differing from each other considerably in colour and greatly in size, 
but agreeing in their general habits. The characteristic marsupium, or abdominal 
pouch, is well developed in some species of Opossum, and only rudimentary in others ; 
and Mr. Waterhouse has consequently divided the genus into two sections, under which 
we may thus characterize the known Central-American Opossums :— 
A. Pouch complete. 
1. D. virginiana. Fur with long stiff projecting hairs; yellowish grey, the face 
lighter, with a dusky mark in front of each eye, and sometimes a trace of a 
median band; ears and tail variably blotched with dark brown and white. 
Length about 22”, of tail 15". 
2. D. aurita. Like the last species; but the long stiff hairs mostly white above, 
and the face with three defined blackish-brown stripes ; ears black, or black- 
* A small Marsupial from Ecuador, named Hyracodon fulginosus by Mr. Tomes (P. Z. S. 1863, p. 51, pl. viii.), 
may represent a distinct family, but it is still only known from the very unsatisfactory original description. 
In any case it will require a new title, the name Hyracodon having been applied to a genus of fossil Ungu- 
lates by Professor Leidy in 1856, seven years before its use by Mr. Tomes. 
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