Here's a nifty website on the Cretaceous trigoniid bivalve, Pterotrigonia
(Scabrotrigonia) thoracica, which is the State Fossil of Tennessee (USA):

http://www.utm.edu/departments/artsci/ggp/geo/fossil.html

The only living genus of trigoniids is Neotrigonia, found in the warm seas
around Australia, and it is a very pretty shell. Lucky Australians!
Australia was on the opposite side of the world when the asteroid hit
Yucatan. North American molluscan faunas were hit hard. Oh, yeah, the
dinosaurs went extinct then too.

A list of other US State Fossils is also given.

Andrew K. Rindsberg
Geological Survey of Alabama