Of the Florida Trachycardium, T. magnum is closest to T. egmontianum. However, the two are easily distinguished. T. magnum lacks the prickly spines that entirely cover T. egmontianum.

Abbott indicates that T. magnum “has been found on the most southerly keys of Florida.” However, I do have two good reports of T. magnum having been found along Florida's east coast. One is from Ken Piech who reports having collected numerous live specimens via SCUBA in 60-70 feet of water off of West Palm Beach in Sep '06 (8 specimens) and Jun '07 (13 specimens). The second report is from Harry Lee, as follows: "We have a bona fide record of Trachycardium magnum (Linnaeus, 1758) from off St. Augustine taken from a scallop trawler by the late Bonnie Holiman in August, 1985. I identified this single valve, which may have ultimately reached the Florida Museum of Natural History." (Note added 10-03-07: In going through some old material I came across a box of Cardiidae I had collected in the early 1980's. Among them was a dead-collected specimen of T. magnum taken via SCUBA on sand in 80 feet of water about three miles off of Palm Beach Inlet, Palm Beach County. So, I now have three good reports of occurrences north of the Keys.)

The first two specimens illustrated in this presentation were graciously loaned from the private collection of Sue Hobbs are from near Pickles Reef off Tavernier Key, Florida Keys in 25-30 feet of water. T. magnum appears to be a deeper water species as opposed to T. egmontianum, which is a common shallow-water species (often exposed during minus tides) found on both sides of Florida and the Keys. So, it appears these two species do not share the same habitat.