shark clam?

[krap101]

i think it was a shark clam. i saw it at my lfs yesterday. it was a pretty big clam. about the size of a clenched fist. i was wondering what these were, because they looked too big to be freshwater, and it said they'd eat small fish

 

[Toirtis]

Sounds like the 'shark-tooth clam' that a number of my LFSes have recently been selling.....not sure of the species, but it is definitely a FW clam...I doubt the predatory claims your LFS has voiced, though.