M. V. Lebour 
449 
Otlier encysted Distotnes have been observed but it is impossible to 
assign to them any position in this scheme as the younger stages are 
not known. These are Gercaria limae Nicoll and Small, G. concava 
Nicoll and Small and a cercaria which I have found frequently encysted 
in the mussels and cockles of Northumberland and the West Coast of 
Scotland, Nicoll (ill. 1907, p. 91) also records an encysted Trematode 
from the skin, muscles, bones and layers of the eye of a Coitus hubalis 
from St Andrews, which was rendered completely blind by the parasite. 
He was not able to identify it. In the same work he also mentions an 
encysted Distomid from the gills of Coitus scorpiiis and Oobius ruthens- 
2 Ktrri. 
I have not myself observed the following two cercariae. The 
descriptions are taken from those of Nicoll and Small (1909, p. 242) 
who kindly allow me to reproduce their figures. 
Gercaria limae Nicoll and Small (1909, p. 242). 
(PI. XXIX, fig. 8.) 
This was found in single isolated cysts in Lima Mans from Millport. 
Cyst spherical, about 0'3 mm. in diameter, with thin opaque membranous 
wall. Cercaria 0‘60 mm. long, elongated oval outline, colourless and 
transparent. Suckers globular, oral sucker 0T2 mm., ventral 0‘152 mm., 
latter situated at the beginning of the postei’ior third of the body. 
Cuticle smooth. Two small oval testes just behind ventral sucker, 
their long axes directed obliquely outwards and forwards. Short 
excretory vesicle. Small pharynx contiguous with oral sucker. In¬ 
testinal diverticula arise immediately behind pharynx and appear to 
terminate near testes. The authors think this is the larval form of a 
Steringophorus or Fellodistomiim, the latter parasitic in its adult state in 
the catfish Anarrliichas lupus and the former in various Pleuronectids. 
Gercaria concava Nicoll and Small (1909, p. 243). 
(PI. XXIX, fig. 9.) 
Found in a young plaice Pleuronectes platessa contained in a small 
round cyst embedded under the skin. It measured 0'17 mm. in 
diameter, very thin-walled so that the cercaria was easily liberated. 
Shape of the cercaria flattened, considerably broader towards the 
posterior end than towards the anterior end. Length 0’48 mm., greatest 
