A crouching lion. In it's right paw is a large key.
Legend,
PAYABLE AT ROBERT KEELING & SONS
Exergue,
GIBRALTAR
A smaller version of the two quartos of 1810 also on this site. You might
want to take a look at it (the two quartos) for a little clearer view of
the reverse.
There's a second copy of this coin on the site
that is in slightly better shape.