344 Trematodes Parasitic on British Fishes. [Sess. 



IX.— SOME TREMATODES PARASITIC ON 

 BRITISH FISHES 



By THOMAS SCOTT, LL.D., F.L.S., Honorary Member. 



{Read April 26, 1911.) 



The Trematoda^ mentioned in the following paper are all 

 Ectoparasites. They are generally found adhering to the 

 gills of fishes, though sometimes on the skin and other parts, 

 but they differ from the more familiar Distomatidse and 

 Trematoda of that kind which are met with chiefly in the 

 stomach and intestines. They are found both on freshwater 

 and marine fishes, but more frequently on the latter. Many 

 of the species are flat and thin, while some are not unlike 

 the scales of fishes, which they seem to mimic. A few of 

 the species are tolerably large, but many of them are small ; 

 and as their colour corresponds to some extent with the part 

 of the fish where they are generally located, they are readily 

 missed. They also differ considerably in shape, for some are 

 nearly circular, others are oval, while others again are narrow 

 and elongated, with the posterior end curiously modified, and 

 in some cases spreading out into a fan-like structure. A 

 curious group are parasitic on members of the Copepod family 

 Caligidse, which in their turn live as the parasites of fishes. 

 Some of the Trematoda have been known for over a century, 

 and one species common on Halibut, especially on Halibut of 

 large size, was recorded and figured by Job. Baster more than 

 a hundred and fifty years ago, in his work ' Opuscula Sub- 

 seciva,' which bears the date 1759. About thirty-one species 

 have been recorded from fishes of various kinds captured off 

 the Scottish and English coasts. 



The Trematoda have been subdivided in various ways by 

 different authors. A work entitled ' Eecherches sur les 

 Trematodes marins,' and containing much interesting infor- 

 mation about them, was published by Professor P. J. van 

 Beneden and Hesse in 1863, in vol. xxvi. of the 'Memoirs 



^ Trematode is a Greek word meaning a hole, referring to the orifices of the 

 suckers. Cf. * Cambridge Natural History,' vol. ii. p. 4 et seq. 



