BRITISH MARINE TURBELLARIA. 217 



reniform. Genital aperture at the base of the tail. The vesicula 

 seminalis contains spermatozoa, which have a central rib, bearing broad 

 triangular lateral membranes, exactly similar to the spermatozoa of 

 Plagiostoma maculatuin. Contrary to Uljanin (41), I find two 

 germaria present. They lie at the middle of the sides of the body. 



Habitat. — In 5 fms., among harbour debris, Plymouth (F. W. G.) 



Distribution. — Sebastopol (Uljanin). 



36. Plagiostoma caudatdm, Levinsen (51). 



Length 1*5 mm. Body when swimming cylindrical, tapering from 

 the middle posteriorly, conical in front. Colour yellow, due to epi- 

 dermal granules. Rhabdites few. Pharynx behind the brain. Eyes 

 large, rhomboidal ; between them a small mass of reticular pigment, 

 with which, according to Levinsen, the pigment-cups of the eyes are 

 sometimes connected. The genital aperture lies a short distance in 

 front of the hinder end. The seminal reside leads by a narrow duct 

 into the cylindrical muscular penis, surrounded by a double sheath, as 

 in PL reticulatum. 



Habitat. — In 5£ fms., Plymouth Sound (F. W. G.). 



Distribution. — Egedesminde, west coast of Greenland (Levinsen). 



37. Plagiostoma vittatdm (Frey v. Leuckart. 23). 



Length 1 — 2 mm. The latter size is that of individuals which have 

 just laid their cocoons, v. Graff ('Monogr.,' p. 391) states that a 

 length of 3 mm. is reached by specimens living on Laminaria below 

 the surface. Jensen also (49, p. 58) finds larger specimens in such 

 localities than at the surface. Tow-nettings taken near shore at Ply- 

 mouth yielded small examples. Body convex above, broadly rounded 

 in front, tapering to a finely pointed "tail " behind. It is well figured 

 by van Beneden (33), pi. v, figs. 1 and 2. Colour more variable than 

 in any other species of Plagiostoma. The typical coloration is three 

 transverse bands of violet reticular pigment on a white ground ; one 

 central, one across the head, and the third across the tail. v. Graff, in 

 his Monograph, pi. xviii, fig. 6, has figured eight different varieties of 



