During the month of November, 1904, I spent a short holiday at the Portobello Fish-hatchery and Biological Station, and on the morning after my arrival the curator, Mr. T. Anderton, brought me a cockle (Chione stutchburyi) evidently infested with some parasite. On examination this proved to be the sporocysts of some species of Distomum containing numerous Cercarice, in most cases just ready to escape from the sporocyst. Subsequently the sporocysts were found in two or three other specimens of the cockle, but, though numerous in those specimens in which they were found, they were not often met with—certainly not in 1 per cent, of the cockles examined.

Similar Cercarice have been long known to occur in various molluscs in Europe, but so far as I am aware the only forms hitherto recorded from New Zealand are the two described by Professor Haswell from Mytilus latus;^* and, as my specimens differ from these and from all the others that I can find descriptions of, I give here a brief description of its general form, mode of occurrence, &c. It appears to come very near to Cercaria villoti, Monticelli (= C. setifera, Villot),^† but differs from that