This is a somewhat standard British socket bayonet - perhaps the Pattern 1839 - modified to fit the "India Catch" utilized on the muskets issued to native contingents in India and other expeditionary forces abroad. They were likely modified between 1840 and 1855. They are typically British in design in that they have a blade "shoulder" and are shallow fullered on the sides; the blade face is flat, without fullered groove.
These are attached by fitting them over the barrel muzzle, and fastened into position by means of a mortise slot, engaging the front site and/or catch.

These were designed to fit the older Brown Bess and variants of the period.

All steel construction.

On this specimen: blade length is about 15-5/8" and socket length is ~3"; back of muzzle displays a stamped production number.
Scabbard is leather with brass throat and drag.