Abstract
Frustulia bahlsii sp. nov. is formally described from soft-water sites from Maine to North Carolina along the eastern United States. The new species is separated from other members of the genus by the following suite of characters: large size, spatulate terminal raphe ends (i.e. not provided with a “porte-crayon”), and coarser longitudinal and transverse striae. Frustulia bahlsii appears closely allied to F. franguellii Manguin (nom. nud.) within the F. rhomboides (Ehrenberg) De Toni group.