A dead dolphin spotted Saturday on the shore of Cape Pogue Pond is not one of the two dolphins that were observed Wednesday and Thursday swimming inshore near the Dike Bridge, a New England Aquarium official said.

Tony LaCasse, a spokesman for the New England Aquarium, said that while aquarium officials don’t yet know how the dolphin died, analysis indicates it had been dead for several days. Mr. LaCasse said the animal measured six feet long and had markings on its fluke that proved it was not one of the dolphins previously observed.

Aquarium officials are studying photographs and measurements of the dolphin taken by on-site volunteers, he said.