Opossum fur is used for a number of flies, usually as dubbing. This is a piece of Australian Opossum fur.
(http://img820.imageshack.us/img820/7493/opo1v.jpg) (http://imageshack.us/photo/my-images/820/opo1v.jpg/)
The buff coloured fur is a substitute for Hare´s Poll,. It can also be used for hackles, tails etc.
It is not always clear which animal is meant, but for older British patterns, it can be safely assumed that an Australian Opossum is meant, but it is often not clear exactly which one, there are a lot of these;
http://en.wikipedia.org/wiki/Didelphimorphia (http://en.wikipedia.org/wiki/Didelphimorphia)
This firm supplies skins of various types if required;
http://www.chichesterinc.com/Opossum-Australian.htm (http://www.chichesterinc.com/Opossum-Australian.htm)
There are a number of these animals. elsewhere as well!
The fur pieces shown below are all natural pieces from opossums! So if you want a particular type or colour, you have to know what it is! With many of these furs it is extremely difficult to even guess what animal it is from.
(http://img716.imageshack.us/img716/7678/opossum1.jpg) (http://imageshack.us/photo/my-images/716/opossum1.jpg/)