I don't recall hearing anything substantive on the matter for about 
six years: 
<https://listserv.uga.edu/cgi-bin/wa?A2=ind0910B&L=CONCH-L&P=R413&X=A36E288A086962535B&Y=shells%40hglee.com>.

Harry


At 11:04 AM 7/30/2015, Derrick Hudson wrote:
>Hello,
>
>     I know this is a very old string, but I'm new to CONCH-L and am 
> catching up. The paper
>Genetics and taxonomy of ribbed mussels (Geukensia spp.), By Sarver 
>et al. 1992 addresses this question fully. As for my experience I 
>believe that G.demissa is the East coast species that spans from 
>Rhode Isaland [sic] to South Florida and that G.granosissma [sic] is 
>the Gulf of Mexico species. I personally have not found any 
>G.demissa North of the Keys.
>
>Derrick
>
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