LARVAL TREMATODES OF THE NORTHUMBERLAND COAST. 447 



sucker, unite for a short space immediately beliind the pharynx, 

 separate again and finally open together in a posterior pore. 

 This Trematode was not found at Stranraer. 



DiSTOMUM (Echinostomum) leptosomum, Creplin (see 

 Plate XL). In the liver of Paliidestriiia stagnalis a species of 

 Echinostomum is found. It occurs commonly in specimens 

 from Fenham Flats, and also at Stranraer ; more frequently in 

 the former locality, 26 per cent, being infected there, whereas 

 only two out of some hundred specimens occurred at Stranraer. 

 This Trematode was found most plentifully in shells from the 

 marshy pools above high-water mark, where there is a good 

 deal of grass, but also in those from the pools left uncovered 

 by the tide for several hours in the day. 



The worm occurs in curiously shaped rediae, which are 

 a pale yellowish colour, gradually becoming colourless to- 

 wards the posterior end. The smallest rediae seen measured 

 o'2 mm. long, and the largest 1*4 mm. They were con- 

 tractile and moved slowly, changing their shape constantly, 

 and were full of cercariae in different stages (see Plate XI. 

 A, B, C). The cuticle is extremely thick, and the anterior 

 part very much wrinkled up into grooves. A pharynx is con- 

 spicuous in young specimens, but an intestine could not be 

 made out. This pharynx, however, in older examples sinks in, 

 and only the anterior opening is clearly seen. A collar 

 surrounds this anterior part, which is peculiarly flat and 

 blunt. The full grown cercaria, which is tailed (see Plate XI. 

 H), is from 0*4 to 0*5 mm. long without its tail (the latter 

 being about o'3 mm. long). In shape and structure it is 

 extremely like the larval Echinostomnm secundum, Nicoll, 

 encysted in the cockle, mussel, and other bivalves, the 

 younger stages of which I believe I have found in the common 

 periwinkle Littorina litt07-ea*, and although this has not yet 

 been proved by experiment, I still hold to that opinion. The 

 size of the cercaria in the periwinkle is about 07 mm. long, 

 and this agrees with those encysted in the cockles' and 



* Northumbei'lancl Fisheries Report for 1905. 



