162 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
C. ALLGocoELA: Family—PLAGIosToMIDa. 
17. Plagiostoma sulphureum, v. Gr. (Pl. XIII, figs. 29,30.) 
Length 2 mm. Body elongate, cylindrical, shghtly 
narrowed and rounded at both extremities. Colour bright 
yellow, due to the rhabdites which lie in the epidermis. 
The mouth and the very small pharynx lie just behind the 
brain. The intestine occupies the central part of the 
length of the body. Opening into the pharynx is a large 
number of pyriform, finely granular cells, apparently 
glandular. Behind these a mass of cells occurs from 
which the ova develope from before backwards. A pair 
of vitellaria lie at the sides of the body, uniting in front. 
The follicular testes, few in number, are sub-central. The 
penis consists of a large proximal vesicula seminalis and a 
terminal muscular tube enclosed in a sheath. The 
spermatozoa, which afford the safest mark by which this 
species may be recognised, have a broad central portion, 
a finely-tapering tail and a cap-like anteriorend. These are 
lateral expansions of the fine, sinuous central thread. 
It is interesting to find this species, hitherto only 
recorded from Trieste, in a coralline tide-pool near the 
Port Erin Biological Station. 
18. Plagiostomavittatum,rey& Leuck.(Pl.XII1 fig.26.) 
Length 1—2 mm. Body rounded in front, tapering 
eradually posteriorly. The colour is usuallyin the form 
of three transverse bands of purple reticular pigment; 
one across the head, another across the centre of the body, 
and a third across the tail. This is the typical form, but 
varieties are almost as abundant as the type. Thus von 
Graff at a single haul among Ulva, at Mullport, obtained 
nine colour varieties. 
The cocoons of this species occur in the autumn. They 
are brown, stalked vesicles, which according to van 
Beneden are attached to the abdominal appendages of the 
