1910-1911.] Trematodes Parasitic on British Fishes, 345 



of the Eoyal Academy of Belgium/ and I have followed gen- 

 erally the arrangement adopted in these ' Kecherches,' but 

 with one or two slight changes, in order to bring it into line 

 with the classification of the Trematoda proposed in vol. ii. 

 of the 'Cambridge Natural History/ published in 1896. 



In the ' Kecherches ' the Ectotrematodes are divided into 

 five families— viz., Tristomidse, Polystomidae, Octocotylidse, 

 Udonellidse, and Gyrodactylidse. In the later work the 

 Udonellidse becomes a sub - family (Udonellinse) of the Tri- 

 stomatidse, and the family Octocotylidae a sub-family (Octo- 

 cotylinae) of the Polystomatidse. All the five families 

 mentioned above have representatives among the species 

 found in British waters. 



Fam. TRISTOMATID^. 



Sub'Fam. TKlSTOMATlNiE. 



The species in this sub-family are provided with a single 

 large disk-like sucker at the posterior end, and with two 

 small suckers in front, one on each side of the mouth. The 

 suckers are on the ventral aspect. 



Genus Epibdella Blainville, 1827. 



Epihdella hippoglossi (0. F. Mliller). 



1776 Hirudo hippoglossi, 0. F. Miiller, ' Zool. Danica/ 

 vol. ii. p. 138, PL LI v., figs. 1-4. 



This Tristoraid is sometimes plentiful on large Halibut, 

 occurring in numbers all over the body of the fish, and it 

 is able to adhere firmly to the skin. It is of an oval form, 

 very thin and flat. The posterior sucker, which is large, 

 is not divided into compartments by raised radiating lines, 

 but the under surface, especially the distal half of it, is 

 covered with minute tubercles. Professor van Beneden states 

 that Baster is the first who makes mention of this parasite, 

 but that, as has happened with others, he took the large 

 posterior sucker for the head.^ 



^ "Memoir sur les vers intestinaux" ('Suppl. des Comptes Kendus,' t. ii.), 

 p. 19, separate copy, 1858. 



