On 7/2/2009 I posted the following inquiry on Conch-L:

"Florida has two species of Dosinea - concentrica (previously elegans) and discus. The portrayal of these two shells has been rather inconsistent among the several books available to everyday collectors. The biggest ambiguity appears to be whether one or the other is an offshore species and the other limited to bays and estuaries. While my experience has both occurring in live populations in bays and estuaries (at inlets), concentrica dominates and discus appears most often found as a beach shell along ocean shorelines. I suspect populations of both wax and wane and that when observations are made may strongly influence impressions. What has been your experience?"

Leslie A. Crnkovic reported his observations:

"I can provide a Texas experiential counterpart for you.

Dosinia discus is available in massive quantities offshore Texas and sometimes litters the beaches in the hundreds of thousands after winter storms. Generically speaking, it is found across the entirety of Texas. I have found it living inside the inlet to Christmas Bay, which is at San Luis Pass, southwest end of Galveston Island. The specimens there tend to be very large. (San Luis Pass is the outlet to the Gulf for west Galveston Bay, the inlet to Christmas Bay is past it in west Galveston Bay)

Dosinia (concentrica) on the other hand is scarce on Texas beaches. Though it has been occasional washed up on beaches from Galveston south, but is typically only found with consistency on South Padre Island beaches, and specimens tend to be small in size.

For me the two species are very distinct and not easily confused... without regard to any habitat considerations."