Mystery fossil

Photograph by Marilyn Susek.

Mystery fossil – Ms. Susek’s father found this fossil in a coal mine in or near Sheffield, England. The rock itself is 7-1/2 cm long x 3 cm wide. I have sent the picture to several knowledgeable people and asked if they could identify the specimen; I received several authoritative answers, not all mutually exclusive. The response I consider most authoritative is – um, never mind; we will save that for later. Can any reader identify the fossil?