194 
Trematodes of Fish 
Otodistomum cestoides (van Ben.). 
This large parasite from the oesophagus of the rays has been 
recorded on two occasions from British waters, first by Miss Lebour 
(1908 p. 39) from Raja radiata and later (as Distomum veliporum ) by 
T. Scott (1909 p. 77) from Raja batis. I have here to record its 
occurrence in Raja macrorhyncha, from which it was collected by 
Ur H. C. Williamson. 
In regard to the life history of this species it is probable that the 
cercaria discovered by Scott, encysted in the stomach wall of the witch, 
Pleuronectes cynoglossus 1 , represents the larva of 0. cestoides. In the 
same fish I have found encysted in the wall of the stomach a cercaria, 
which from its large size and general structure cannot be referred to 
any other species. It occurred as a large orange-yellow globular cyst 
1'95 mm. in diameter, firmly attached to the outer wall of the stomach 
by a short pedicle. The wall of the cyst consisted of a thick tough 
outer coat within which was a large amount of viscous yellow material. 
The cercaria measured 2'4 mm. in length, with a maximum breadth 
across the ventral sucker of 0'66 mm. Both suckers were trans¬ 
versely elongated, the oral measuring 0 - 29 x 0'35 mm. and the ventral 
0 - 43 x 0'59 mm. The latter was situated at a distance of 0'96 mm. from 
the anterior end. The pharynx was small and situated close to the oral 
sucker. There was a very short oesophagus and wide diverticula 
extending in a slightly sinuous manner to the posterior end of the 
body. The excretory vesicle was Y-shaped and consisted of a median 
stem extending a quarter of the length of the body, and two lateral 
branches reaching forward as far as the pharynx. No other organs were 
visible. 
REFERENCES. 
Lebour, M. Y, (1908). Fish Trematodes of the Northumberland Coast. North¬ 
umberland Sea Fisheries Report for 1907 (1908), 11-57. 
Nicoll, W. (1907). A Contribution towards a knowledge of the Entozoa of 
British Marine Fishes, Part 1. Ann. Mag. Nat. Hist. Ser. 7. six. 66-94. 
Odhner, T. (1911). Zum natiirlichen System der digenen Trematoden III. Zool. 
Anzeig. xxxvm. 97-117. 
Scott, T. (1909). Some notes on Fish Parasites. Tiventy-Eighth Annual Report 
Fishery Board Scotland , Part 3, 73-92. 
1 In Scott’s paper this species is inadvertently named P. microcephalus. 
