While touring the Natural History section of the Arizona Historical Society Museum at Papago Park (1300 N. College Ave, Tempe Arizona 85281) I saw this clam fossil specimen (AHS-NH#21712)
This fossil was probably found in the Pierre Shale Formation of Glendive, Dawson County, Montana, USA. It dates to the Cretaceous Period.
Image was taken in October 2014.
Sources:
Neat image of Cretaceous Inoceramus clam fossil with pearls
http://www.paleocurrents.com/baculite_mesa/img/2003-05-17mesa_fossils/HTML/img_2480.htm
