Posted: Aug 12 2009, by Harry Lee:

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I believe there are several synonyms for this species. and Sphenia dubia (H. C. Lea, 1843) appears to be the earliest. This, like other nestlers, is quite variable conchologically. Recent shells we attribute to this species cannot be separated from those of this Miocene fossil. S. attenuata Dall, 1898, and Sphenia antillensis Dall and Simpson, 1901 are apparent synonyms from the Pliocene and Recent faunas respectively. Coan (1998) states that the E. Pacific S. fragilis Carpenter, 1857 is synonymous with our (Recent) taxon, which he distinguishes from the above two fossil taxa (Coan, 1999). Observed in abundance attached to wave-dashed intertidal rocks in Flagler Co. (HL!); also St. Lucie (Lyons, 1989b), Pinellas Cos.; NC, GA, Brazoria Co., TX (all in my collection). Enlarges known range for the genus vs. Abbott (1974): “South Padre Is. ...Brazil.”

Coan, E.V., 1998. The eastern Pacific species of Sphenia (Bivalvia: Myidae). Abstracts of the World Congress of Malacology, Washington, DC 25-30 July 1998. Chicago, 1998.