MEMBERS of the family Physidae a-re among the most ;common and widespread fresh-water mollusks in Puerto Rico and are frequently associated with Au8stralorbis glabratus, intermediate sna,il host of Schistosoma imansoni. In several recent papers on the ecology of A. glabratu,s in Puerto Rico (1-4) and in a key to the fresh-water mollusks of Puerto Rico by Van der Schalie (5), the only physid referred to is Phy&a cubensis Pfeiffer. Ferguson and Richa,rds (6) reviewed listings of phys,id mollusks from Puerto Rico by earlier collectors (including severa,l species of Physa and Aplexa), confirming P. cubensis and adding Aplexa marmorata (Guilding) from recent collections. As a potential intermediate host of Fasciola hepatica, P. cubensis (7) must be differentiated from Aplexa if molluscacidal control of sheep liver fluke disease, is attempted locally.