M. V. Lebour 
451 
{d) Monostomum group. 
Gercaria ephemera Nitsch {= Monostomum flavum Mehlis), 
Lebour (1907 c, p. 436). 
(PI. XXIX, figs. 11, 12.) 
This cei'caria is not the larval form of Typhlocoelmn Jiavum (Mehlis) 
as was formerly thought: the ends of the forks of the alimentary canal 
are not joined as they are in that genus. I have therefore returned to 
the name Gercaria ephemera given by Nitsch. It occurs in the digestive 
gland of Paludestrina stagnalis from Fenham Flats and Loch Ryan ; 
in about six per cent, from Fenham Flats and 20 per cent, from Loch 
Ryan in August and November. The redia is yellowish with a dark 
brown intestine, well developed pharynx but no thickening round the 
mouth. It is active and contains cercariae in all stages. 
The cercaria measures 0 24 mm. in length without its tail which is 
slightly longer than the body. It is opaque and speckled with brown 
with a brownish tinge all over the body. Anteriorly there are three 
conspicuous eye-spots arranged in a triangle. The body at each side of 
the base of the tail is drawn out and provided with a small sucker-like 
structure which apparently helps to fix the cercaria whilst the anterior 
part of the body is extended. The oral sucker is large and leads to the 
oesophagus which bifurcates just behind the anterior eye. There is 
no pharynx. The lobes of the intestine extend nearly as far as the 
posterior end of the body. The excretory vesicle is a clear sac at the 
hind end of the body with two conspicuous lateral canals full of clear 
granules opening into it. 
The further life-history is not known but it apparently belongs to 
the family Notocotylidae Lhe., which live in the intestinal caeca and 
rectum of sea birds. Ltihe (1909, p. 178) thinks it may be Notocotyle 
triseriale Dies, or Gatatropis verrucosa (Frol), both of which live in a 
variety of sea birds, more particularly ducks. This species is perhaps 
identical with Gercaria imbricata Looss which he regards as the larval 
form of Notocotyle triseriale Dies. (1896, p. 192). G. imbricata occurs 
in Bythinia tentaculata. The usual habitat of G. ephemera is Planorbis 
Cornells a purely fresh water Mollusk. 
Gercaria lophocerca Fil. (Lebour, 1907 C, p. 443). 
(PL XXIX, figs. 13-15.) 
This peculiar cercaria occurs in the digestive gland of Paludestrina 
stagnalis from Fenham Flats (in about 40 per cent.) and Loch Ryan 
(15 per cent.) and also occurs in the digestive gland of the periwinkle 
