Larval Trematodes. 243 



the absence of oesophagus (althougli this may be due to con- 

 traction) are strong evidences in favour of Fdlodistomum 

 fellis (Olss.) being the adult; the only coatra-indication to 

 which is the fact that Anarrhic/ias lupus, the only known 

 host of Fellodistomurn fellisj is not common in the neighbour- 

 hood of Millport. 



Cercaria concava, nov. 



In a young plaice {Pleuronectes platessa), about 41 inches 

 long, a small round cyst was found embedded under the skin. 

 Its diameter was '17 mm. and it was very thin-walled, so that 

 the cercaria was easily liberated. Its resemblance to Crypto^ 

 cotyle concava (Orepl.) is even at first sight very striking. 

 The shape is flattened, considerably broader towards the 

 posterior end than towards the anterior end. The length is 

 •48 mm. and the breadth at the widest part "22 mm. The 



Cercaria concava. 



small round oral sucker has a diameter of "06 mm., the pre- 

 pharynx is '03 mm. long, the pharynx "04 mm., and the 

 oesophagus "04 mm. The diverticula have the shape 

 characteristic of the adult Cryptocotyle, bending in towards 

 the middle line in the vicinity of the genital sucker, then 

 curving out, and finally turning in at their termination to 

 approach each other. The excretory vesicle is clearly seen 

 and consists of two fairly straight lateral tubes, beginning 

 near the prepharynx and running into a simple, rather wide 

 terminal sac at the posterior end of the body. The genital 

 sucker is quite distinct, situated about the middle of the body. 

 That this structure is not a ventral sucker in the true sense 



