STUDIES ON THE DIGENETIC TREMATODES. 4.73 
reaches of the intestine (duodenum and ceca) of Pleuro- 
nectes microcephalus, the lemon-dab, from the Firth of 
Clyde. It differs in several respects from St. furciger 
(Olss.), which is found so commonly in many Pleuronectid 
fishes in the North Sea. 
In life the animal is capable of great extension and con- 
traction, but on being killed or on being allowed to die in its 
natural habitat it assumes a fairly regularly oval outline, 
always more pointed towards the anterior extremity. It is 
considerably flattened and has a rather delicate, transparent 
appearance. Living specimens have a distinctly reddish 
colour, not so deep as that of St. furciger. 
The length is 1-5-2 mm., but none of my specimens seem to 
be fully mature, so they may attain a larger size. The 
breadth is about two fifths of the length—6—8 mm. Cuticle 
unarmed. The oral sucker invariably lies a short distance 
from the extreme anterior end, and it is usually elongated in 
the lone axis of the body. It measures about °22 by 15 mm. 
The ventral sucker is almost exactly twice as large, its 
diameter being -44 mm. in a specimen of 2 mm. length. It 
is situated a little behind the middle of the body, and it this 
respect it differs from the position in St. furciger, in which 
it is in front of the middle of the body. 
The pharynx is immediately behind the oral sucker and 
measures ‘085 mm. in diameter. ‘I'he cesophagus is twice as 
long as the pharynx, sometimes slightly more, sometimes a 
little less than that. This feature, again, distinguishes the 
species from St. furciger, in which the cesophagus is about 
the same length as the pharynx. The diverticula are simple 
and extend a little beyond the testes, but not so much as in 
St. furciger. 
The excretory vesicle is perhaps the most obvious diagnostic 
feature. It is Y-shaped, but the unpaired portion is very 
short, so that it sometimes appears almost V-shaped. The 
paired limbs extend forward to the level of the pharynx. It 
is distinctly mapped out by the refringent nature of its 
contents, butis not so conspicuous as in St. furciger. 
