The obsolescence of radial sculpture on the last whorl of the land snail Ancotrema hybridum (Ancey, 1888) has been used to separate it from A. sportella (Gould, 1846), but shells are sometimes difficult to assign to one species or the other, prompting questions about their species status. Factor analysis of shell characters of 311 specimens of Ancotrema Baker, 1931, including characters of surface sculpture strength, shell size and rib density, revealed continuous variation of these characters without bimodality. Radial sculpture begins obsolescing at about whorl five, so shells that stopped growing near whorl five have A. sportella-like morphology, while those that continued growing after whorl five have A. hybridum-like morphology. We saw no meaningful differences in the genital anatomy that would suggest different species. The obsolescence of sculpture beginning about whorl five regardless of ultimate whorl number, lack of bimodality of shell characters, and lack of anatomical differences lead us to conclude that the two forms are a single species. Ancotrema hybridum is a junior synonym of A. sportella.
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Vol. 59 • No. 1