Somewhere on this site, I'd noticed that Marlo wanted information on Trachycardium isocardia in Florida.
I found them up Sebastian Inlet where it meets the Indian River, and at Peanut Island.
I thought Marlo got the specimens but they may have been lost prior to Marlo getting the batch of shells I'd earmarked for him.
Shells were abundant with sand and grass about a mile southwest of the Sebastian Inlet bridge and near the the rapidly moving flow between the River and Inlet (1980s). These were T.i, not T. egmontianum. This area is at the "north" side of the Inlet and getting there requires a long rough wade, even at low spring tides. Huge Melongena corona are found on oyster bars in the same general area. Many other species are found as well in the grass, algae and substrate.
At Peanut Island both isocardia and egmontianum were found popping out of the sand on the bars (1970s through 1990s).
My experience with these kinds of finds is that there may be years of absence followed by blooms and relative abundance. I also used the advantage of the very low tides - the product of winds and spring tides.

Phil

Phil,

I've heard stories from the older commercial clammers from Cocoa and Cape Canaveral that what they describe might be T. isocardium was once found in the Indian River from Sebastian to Titusville. However, I've never been able to obtain specimens. All the Trachycardium you gave me were either T. muricatum (most of them) or T. egmontianum. I had Harry check out any that were questionable. I've seen nothing collected in east Florida lagoons that would compare to the deep water T. isocardium I have for comparison. Personally, I'm not convinced T. isocardium is not actually a deep water variant of T. egmontianum.

Trachycardium isocardia from Florida

Marlo.
If you don't have the specimens with the data, we'll get nowhere. I'm sure I wouldn't mistake a muricinum or egmontianum for an isocardium. I was never confused by questionable specimens. They were distinct. Without a collection to draw from, however, I may as well bow out on these issues.
Phil