LARVAL trf:matodes of the Northumberland coast. 439 



Echinostomiini secundum, Nicjll, from the cockle and mussel^). 

 In the Crustacea almost any part of the body seems to be 

 suitable. In Carcinus uiceiias they have been found in the 

 nerve sheaths, the digestive organs, etc.,|| and in certain 

 amphipods almost the whole of the inside of the body is 

 crowded with them. 



Seven larval forms are here described, six of which are from 

 Paludestrina stagnalis, Basterot, or as it is more commonly 

 called Hydrobia ulvce, Penn. Two of these belong to the 

 genus Monostomum, and the others appear to be Distoma of 

 various subgenera. One which I have provisionally named 

 Cercaria ubiquita on account of its occurring in three different 

 species of Mollusca, I am somewhat doubtful about, as I 

 cannot find any ventral sucker. I place this form for, the 

 present under Distomum, as it bears such a strong resemblance 

 to Cercaria microcotyla of Filippi, which has a very small and 

 inconspicuous ventral sucker. It is also like C. vtrguia, 

 Filippi*. I have given provisional names for the sake of 

 convenience to those cercariae which I cannot find described. 

 These are Cercaria ubiquita, C. piruui, and C. oocysta. 



It is interesting to note that the cercaria which I believe to 

 be Echinosfoviuui leptosomum, Creplin, is extremely like the 

 same stage in E. secundum, Nicoll. The arrangement of the 

 organs is identical, and also the number of head spines ; it is 

 only by a, slight difference in the lengths of some of these 

 latter, and in the size of the animal that a distinction can be 

 made, yet the rediae from which these two species are 

 developed are absolutely dissimilar. 



Another interesting fact is the occurrence of the Trematodes 

 Monostomum flavum, Mehlis, and M. lophocerca, Filippi, in 

 Paludestrina stagnalis, which, although fond of brackish 

 water, is here distinctly marine, being covered by the tide 

 twice a day for several hours. The few freshwater streams 

 which flow into the sea do not occur just at this point, 



X Villot, Ann. des Sci. Nat., Se'r. VI., Tom 8, 1879, and Nicoll, Ann. and Mag. of 

 Nat. Hist., Jan., 1906. 



II Mcintosh, Journal of Microscopical Science, V., N.S., 1865, p. 201. 



* Filippi, " Mem. p. servir a I'hietoire genetique des Trematodes," Turin, 1851-5. 



