348 Trematodes Parasitic on British Fishes. [Sess. 



the circumference inwards ; the average number of rows 

 appears to be about twenty. It is also provided with a 

 minute supplementary disk — the adhesive disk — which is 

 situated on the lower edge of the sucker, and in line with 

 the middle of the body. In one species the adhesive disk 

 is tongue-shaped, but is circular in the others. Moreover, 

 in the species mentioned above the adhesive disk is outside, 

 and just touches the circumference of the large sucker ; while 

 in another species it is inside the circumference, and there are 

 also other slight differences. 



In its general form A. monticellii is moderately narrow and 

 elongated, and measures about six mm. in length. It was 

 obtained on the gills of a Thornback Skate captured in the 

 North Sea. Another species, not determined, but which 

 appears to be new, was obtained by my son when trawling 

 off the Welsh coast. It occurred in washings of trawl refuse. 

 Most of the species hitherto recorded have been obtained on 

 Skates and Eays. 



Sul-Fam. Monocotylin^. 



The species in this sub-family have a large posterior sucker, 

 but they want the small anterior pair with which the Tristo- 

 matidse are furnished. Three species belonging to this sub- 

 family have been obtained on British fishes — viz., Calicotyle 

 Kroyeri, Calicotyle ajffinis, and Heterocotyle pastinacm. 



Calicotyle Kroyeri Diesing-^ has been recorded by several 

 observers, and does not appear to be very rare. Kroyer, 

 after whom the species is named, discovered it in the cloaca 

 of Raia radiata captured in the Kattegat, and it has been 

 obtained near Shetland and off Aberdeen on the same species 

 of Skate. It has also been found in the same situation on 

 Baia clavata captured in the Firth of Clyde and in the Irish 

 Sea. 



Calicotyle affinis T. Scott was obtained on the gills of 

 a Chimcera monstrosa captured in the North Sea in January 

 1910, and appears to be comparatively rare. It is larger 



^ CaUicotyle with two Vb has sometimes been used (see ' Recherches ' ah-eady 

 referred to and my own papers), but the form adopted by Diesing, who instituted 

 the genus, is Calicotyle. 



