You're welcome, but it pays to ask someone who actually knows NY guns.
So I did, and Bob Naum, one of two living NY rifle guys, said this:
HYSLOH & SON, ROBERT
NYC 1834
Robert Hysloh was a merchant from 1794 on, and seems to have dealt in gun materials among other things. Locks stamped “R. Hysloh New York” are not uncommon. He was partner in the firm of Irving, Smith & Hysloh in the late 18-teens. They are not listed among those burnt out by C. Foster in An Account of the Great Conflagration (N.Y., n d) though 6 Exchange. In 1834 the firm becomes Robert Hysloh & Son: Hysloh & Son Robert, merchants 6 Hanover h. 55 Beach Hysloh William I 6 Hanover h. 55 Beach 1835 merchants 6 Exchange-plh. 55 Beach Wm. I 6 Exchange-pl h 55 Beach 1836 Hysloh & son Robert mers. 220 Pearl h. 55 Beach Hysloh William I 220 Pearl h. 103 East Broadway 1837.
Someone mixed up p and h
Me, I write on Michigan Gunsmiths. In 1860 about 40% of our smiths had come from New York state, so it behooves me to know something about NY guys.