That specific form of buckle, made of thin stamped sheetbrass, consisting of a "bow" which swivels on another bow with two tiny sharp-pointed teeth, was made for use on CLOTH straps on clothing. Note that the tiny sharp-pointed thin teeth are not suitable for use on leather straps. Its inventor, Sheldon S. Hartshorn, was awarded US Patent #13,218 for his design, on July 10, 1855. (His patent was renewed in 1874, to keep it legally enforceable.) So, technically, it is known as a Hartshorn's Patent 1855 clothing-strap buckle. https://www.google.com/patents/US13...a=X&ei=sBxEVO3IF4rdsASdqoH4Bg&ved=0CB0Q6AEwAA
Hartshorn's Patent buckles were manufactured for many decades after invention in 1855, so time-dating one is difficult. Yours has a slight modification (to increase the strength of the toothed area) from the original design shown in the 1855 Patent's diagram (below), so it is a somewhat later version.