Extinct fossil Dichocoenia caloosahatcheensis extremly large has been cut with wet saw to where it would sit flat.

Lengtht: 7 1/2" inches
Width: 6 1/4" inches
Fort Denaud Member, Caloosahatchee Formation, Collier County, Florida, USA
Scroll down for more pictures, put mouse over picture of fossil and zoom in the upper picture.