Manhatten Arms Co. was a "trade brand" used by Schoverling, Daly & Gales on all manner of low to medium priced guns. There were cheap Belgian hammer guns, Hunter Arms Co. Fultons, and somewaht better European guns all sold at one time or another under the Manhatten Arms Co. name. My Father use to have a Damascus barrel 10-gauge marked Manhatten Arms Co. that was obviously a generic Birmingham boxlock.

Hopefully, Drew will be along with a more complete answer.