W. Nicoll 
347 
necessitates some slight modification of the definition of that sub¬ 
family. It is more closely related to Lepocreadium than to Lepidapedon, 
and it is only separated from the former by the shape of the oral 
sucker, the presence of pigment patches, the short prepharynx and the 
presence of the pseudo-oesophagus. The changes which might be 
suggested in the definition of the sub-family are as follows: 
Includes forms of 1—6 mm. in length; ventral sucker feebly 
developed and usually smaller than the oral sucker ; prepharynx usually 
elongated but may be short; initial parts of intestinal diverticula may 
be fused to form a pseudo-oesophagus; Laurer’s canal not arising 
directly from the receptaculum seminis. 
The last-mentioned feature is a further point of distinction between 
this sub-family and the Allocreadiinae, in which Laurer’s canal 
arises directly from the distal end of the receptaculum seminis. 
Sub-family V. Fellodistominae Nicoll 1909. 
Genus i. Leioderma Stafford 1901. 
Synonym. Steringophorus Odhner 1901. 
I have hitherto used the name Steringophorus for this genus, but 
Stafford’s name has priority, although at the same time his definition 
is inadequate. 
Species 1. Leioderma furcigerum (Olsson 1868). 
This species is evidently not nearly so common in the Firth of 
Clyde as on the East coast. It was found only in Pleuronectes limanda 
in 33 per cent. Taking all the Pleuronectidae examined, its occurrence 
was only to the extent of 12 per cent. In my experience it is twice as 
common on the East coast and according to Miss Lebour it is four 
times as common on the Northumberland coast. Its place in the Firth 
of Clyde appears to be taken to a large extent by the allied species 
Leioderma cluthense. On the South coast of England it seems to be 
entirely replaced by that species. 
A very full account of the form is given by Odhner (1901, pp. 305— 
310) and Miss Lebour (1908, pp. 53—55). 
Species 2. Leioderma cluthense Nicoll 1909. 
This species was found in every specimen of Pleuronectes microce- 
phalus and in no other host. A fairly complete description has already 
been published (Nicoll, 1909 a, pp. 172—175). 
