Dysnomia lewisii Walker, 1910 The forkshell or Lewis pearly mussel, scientific name Epioblasma lewisii, was a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.

[2] Its natural habitat was shallow riffle-beds of large rivers.

[2] This habitat was largely destroyed by dam construction and canalization, and the last populations of this species died sometime during the middle of the 20th century.

Only a single museum specimen was collected that preserved the internal soft tissues.

[citation needed] It appears to be closely related to Epioblasma flexuosa, which is also now extinct.