Sharon - I've included the Panther description which I found on the Cartier website. You will have no problem selling a genuine piece of Cartier Jewelry from the House of Cartier.
Authenticity will be your biggest hurdle. Is it marked? I'm guessing you don't have any documentation or proof of purchase. It should be signed Cartier. I would love to see this piece - If you have photos I can manage your valuation. Sharon, do you have photos? A prospective buyer will need to see photos and so will the online appraiser.
Warm Regards Yvonne
"A truly wild animal, the Panther is more than a mere symbol for Cartier. It is a timeless icon that is both predatory and elegant, restrained yet always ready to pounce. Roaming free with emerald eyes, onyx muzzle and diamond-set coat, the creations from the Panther Collection make their mark on the world of jewelry."