Abstract
Extensive series of Amphidromus Albers, 1850 were collected from low-altitude areas (30–500 m above sea level) in Thailand, Laos, Malaysia, Singapore and Indonesia between 1993 and 2004. Data on shell colour, genital and spermatophore morphology, and radular structure are presented. Five species of Amphidromus (Amphidromus) are reviewed, of which four occur in Thailand. Intraspecific variation between populations of Amphidromus (Amphidromus) atricallosus (Gould, 1843) is considered; three subspecies are accepted and a new subspecies described. Subspecies of A. (A.) inversus (Müller, 1774) and A. (A.) schomburgki (Pfeiffer, 1861) are reconsidered, and a new subspecies of the latter is described. A dichotomous key to the species and subspecies of Amphidromus (Amphidromus) in Thailand is provided.