I concur with Mike Irwin in that it's most likely an 1873 Ordinance revolver. Here is a Wikipedia article on the revolver we think it is:
This revolver is probably most widely known for the pair of them that Brendan Frasier used in the film The Mummy.
I've wanted one of these interesting revolvers ever since seeing that movie as a kid and for $150, I would certainly buy it were I in your shoes.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar