LARVAI- TREMATOBKS OF THK NOUTHUMHKRLAND COAST. 445 



of 50 from Stranraer and two out of six from Budle Bay, 

 Northumberland ; and in two out of 50 Littorina rtidis from 

 Stranraer. It has not yet been found in the Northumbrian 

 Z. rudis. 



This species is very Uke Cercaria mici-ocotyla described by 

 Filippi, but his is much smaller (0-004 rnm. in length, includ- 

 ing the tail), and has two brown spots posteriorly. His 

 specimens came from the freshwater mollusks Paludina vivi- 

 para and P. achatina. There is a small ventral sucker in his, 

 and it seems likely that there is really one present in the 

 species here described, though it is very difficult to see. 



Cercaria oocysta (see Plate X. E, F, G). In the liver of 

 Paludestrina sfagnalis, both from Fenham Flats and Stranraer, 

 a cercaria - occurs, which from its oval cysts I shall call 

 Cercaria oocysta. It is enclosed in thin walled sporocysts of 

 no definite shape, and it encysts in these in colourless trans- 

 parent oval cysts measuring 0*12 by 0*07 mm. The curious 

 fact that the cercaria encysts in the same sporocysts in which 

 it was developed was noticed by me in a Trematode occurring 

 in Cardhim edule^, where tailed cercariae were seen in the 

 sporocysts at the same time as encysted forms. In the present 

 case it is much the same, for unmistakably tailed cercarige, 

 although not fully developed, were found within the sporocysts 

 along with those which had already encysted, and there were 

 also separate bodiless tails wriggling about. The sporocysts 

 with cercarise are packed closely into the liver — the cercariae 

 occurring in hundreds. Many of the cysts appear to be free, 

 the walls of the sporocysts having probably burst or been 

 dissolved away. The cercaria lies curled up in the cyst, and 

 when pressed out measures 0*24 mm. long. In shape it is a 

 long oval, being about 3^ times as long as it is broad. The 

 anterior sucker measures o'02 6 mm. across, and leads by a 

 thin straight tube to a small pharynx which is almost midway 

 between the oral sucker and the bifurcation of the intestine, 

 but slightly further forward. The short lobes of the intestine 



* Annals and Magazine of Natural History, Jan., 1907. 



