Abstract
In 1931 Dr M. V. Lebour drew my attention to a larval Trematode (one of the “Hugetailed Monostome” group of H. M. Miller, 1925) which occurred quite frequently in Turritella communis from the Rame Mud, Plymouth. During 1932–4 I examined 541 Turritella communis from the same locality and an 8 per cent. general infection with four species of closely related cercariae was recorded, but the species which was common the previous year did not occur once. 180 Turritella communis from Naples revealed a 5 per cent, infection of two other closely related species.