The freshwater pulmonate family Physidae is represented in Britain and Ireland by two naturally occurring species, Aplexa hypnorum (L.) and Physa (Physa) fontinalis (L.). Physella (Physella) gyrina (Say), a species native to North America, has recently been reported from Lough Neagh in Ireland and there are earlier records for western Britain (Anderson 1996). Another putative North American species, Physella (Costatella) acuta (Draparnaud), is widespread in Britain and is reported also for the first time from Ireland. Unlike gyrina, the home range of acuta in North America is unknown and there is confusion about its identity there. A case is made for synonymising Physella heterostropha (Say), native to the eastern and south-eastern US, with P. acuta. The current state of taxonomy in the subfamily Physinae is briefly discussed.