It looks like NA 112 in Albert's book. This is the description given;
NA 112 Navy 2-piece with border and circle of rope.
A. The device, eagle facing left, upper fluke of anchor behind left wing. "R & W. Robinson/Extra Rich"; 23mm; pre-1850. RV 3 (There are many post 1850 makers and variants, as this pattern was in use until 1941.)
I hope, for you, it turns out to be an early button.