SN's were not required at that time. If it has one, look on the butt or frame.
£150
about the the late 1800s
Pistol made by Hopkins and Allen @ turn of the century or before.
No definitive sn data published.
No known published examples.
Hopkins & Allen Company.
They made thousands of them.
Try Hopkins & Allen. Depending on condition, anywhere from $25-100.
Try Cornell Publications.
10-100 USD or so
A bulldog .44 spl cal
You will need a professional appraisal.