68 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



C. ALLffiOCOELA : Family — Plagiostomid^. 



17. Plagiostoma sulphureum, v. Gr. (PL XIII, figs. 29,30.) 

 Length 2 mm. Body elongate, cylindrical, slightly 



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 anterior end. 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. PZa^iosto7?^rt'yi2^?^aiz^7?^Frey&Leuck.(Pl.XIII,fig.26.) 

 Length 1 — 2 mm. Body rounded in front, tapering 



gradually posteriorly. The colour is usually in 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 Millport, obtained 

 nine colour varieties. 



The cocoons of this species occur in the autumn. They 

 are brown, stalked vesicles, which according io van 

 Beneden are attached to the abdominal appendages of the 



