M. V. Lebour 
435 
Gercaria halani mihi (1908 a, p. 10). 
(PL XXVI, figs. 15, 18.) 
Occurs encysted in the common barnacle Balanus balanoides from 
Budle Bay and Fenham Flats. The cyst is thin-walled and spherical 
(fig. 16), 0'04 mm. across. The cercaria is pale yellow and when pressed 
out of the cyst measures about 1 mm. in length. Very long prepharynx, 
longer than the oesophagus. Intestinal caeca reaching to just beyond 
the posterior border of the ventral sucker. Body covered with spines 
even at the posterior end. 
It is interesting to note that small cysts with very thin walls are 
found with these large forms in Balanus and inside are curled up 
cercariae with stylets very like Cercaria ubiquita. This seems to show 
that the same kind of cercaria enters the Balanus and grows into the 
Spelotrema form. 
Some time ago I suggested (1908 A, p. 10) that this was the encysted 
Spelotrema excellens but now think that the form so commonly found in 
the crab is much more likely to be this species. 
The further life-history is not known. 
Cercaria littorinae-rudis sp. inq. 
(Lebour, 1906, p. 6.) 
(PI. XXVII, figs. 3-7.) 
This cercaria was found only once occupying the digestive gland of 
a specimen of Littorina rudis from Holy Island, Northumberland, in the 
beginning of May. It is a specially interesting form as it shows a 
Trematode most certainly belonging to the Spelotrema group but yet 
with such a different form of cercaria, for no tail was observed and it 
probably has none. In form of the sporocysts and habit of the cercaria 
it is much more like Gymnophallus. Pelseneer (1906, p. 171) found in 
Natica alderi from Boulogne cercariae very much like these in similar 
sporocysts but there were much fewer cercariae in each. 
The sporocysts are pale yellow and spherical about 1 mm. across and 
are full of cercariae more or less doubled up. This doubling up or 
folding is interesting as they closely resemble Gercaria ubiquita in this 
way. The cercaria (fig. 5) when extended measures 0'25 mm. in length 
and the body is covered with spines except at the posterior end. 
Unfortunately I have not got more detailed measurements of this 
species. The prepharynx is much shorter than the oesophagus. 
