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Description
The hinge plate and teeth are lacking in this species as they are in all members of the genus Anodonta. Umbos extend above the hinge line. The alewife floater is easily distinguished from the eastern floater, Pyganodon cataracta, by the former having a pronounced thickening of the shell below the pallial line in the anterior-ventral region. The periostracum is generally smooth and may range in color from yellow to brown-black. Young individuals may have green rays over the surface of the shell.

Distribution (see map)
The alewife floater ranges from Nova Scotia and New Brunswick, Canada, to the Potomac River in Virginia and Maryland (Johnson 1946, 1970, Burch 1975). A disjunct population is also known from the Chowan River in North Carolina (Shelley 1983). William Adams (pers. comm.) found live individuals in the Chowan River during the Summer of 1989. This species has also been documented from the Roanoke River below the last dam at Weldon down to Washington County.

Distribution by County: Chowan River Basin: Hertford Co. (Meherrin River, Chowan River); Gates Co. (Chowan River). Roanoke River Basin: Northampton Co. (Roanoke River); Washington Co. (Roanoke River). NOTE: All headwater areas that flow into these occupied habitats should receive special management.

Habitat Preferences
Johnson (1970) states that this species appears to prefer clean sand/gravel substrates in relatively fast flowing water. However, at the Chowan River, NC site the water has an almost imperceptible flow (B. Adams, personal communcication).

Life History
The alewife (Alosa pseudoharengus) appears to be the alewife floater's dominant fish host (Johnson 1946). According to Ortmann (1911), all Anodonta species appear to be bradytictic (long term brooders).