It looks like a little pocket pistol or ladies' muff pistol. These were made by the thousands here and in Europe mostly by makers who did not think enough of the guns to put their names on them. They were the mid-19th century equivalent of the "Saturday Night Special".
They were very common and a lot are still around. In working condition, and without some special provenance (such as proven ownership by a famous person), they go for around $100-150 in antique shops as novelties. Alas, most are not in working condition and their value is nominal.
Some call this type of pistol a "derringer" but they are not of the Deringer type.
Jim