I checked a chart of London gold marks. To me, the marks look like a leopard (London) with the head of a woman wearing a crown. That’s the year Queen Victoria was inaugurated, 1837. Google London gold marks to find a chart and check it out.
If this is the case and I were you, I’d find a jeweler that deals in historic jewelry and get her opinion. If the pearls are original to the clasp, they’ll be natural, non-cultured pearls unless they are coated glass.