426 
Marine Cercariae 
Gasterostomum sp. 
Bucephalus syndosmyae sp. inq. 
(PI. XXV, figs. 5, 6.) 
This cercaria occurred once out of five specimens of Syndosmya alba 
from Millport, Scotland, in July. Pelseneer (1906, p. 176) records 
Bucephalus haimeanus from this Mollusk, but this is certainly distinct. 
The sporocysts riddled the whole animal but especially the digestive 
gland and region of the gonad. They are very long, thread-like and 
unbrancbed and contain cercariae in all stages (fig. 5). The full-grown 
cercaria w^hich was bursting from the sporocyst is very like B. haimeanus 
(fig. 6). The ventral sucker (0 01 mm. across) which leads to the 
sac-like intestine is behind the centre of the body instead of in front. 
The bod}^ is covered with small spines. Anteriorly is a sucker-like 
cystogenous organ 0'03 mm. long by 0'02 mm. broad, or circular 
according to the state of contraction. Posteriorly is the tail with long 
processes. The centre of the tail is partially divided posteriorly by an 
indentation. 
Further stages of the life-history are not known. 
Besides these cercariae are to be noted encysted Gasterostomatous 
Trematodes found by Johnstone (1904, p. 103) in the muscles of small 
plaice. These were sexually mature and the uterus was full of eggs. 
This wmrm seems more nearly related to the genus Prosorhynchus than 
to Gasterostomum. 
II. Prostomata. 
1. Cercariae developed in sporocysts. 
(a) Gymnophallus group. 
Genus Gymnophallus Odhner. 
Cercaria margaritae sp. inq. (=the Pearl Trematode 
of Jameson (1902)). 
(PI. XXV, figs. 7, 8.) 
This is referred by Jameson to Leucithodendrium somateriae 
(Levinsen) but Odhner (1905, p. 312) thinks it resembles Gymnophallus 
hursicola more closely, and Nicoll (ix. 1907, p. 265) is of the opinion 
that it may be G. dapsilis. It is extremely difficult without infection 
