216 F. W. GAMBLE, B.SC. 



close to the binder end. The male organs were not thoroughly- 

 developed in either of my two specimens, and the form of the mature 

 spermatozoa remains unknown. The germaria lie at the sides of the 

 posterior third of the body. The yolk-glands form narrow-lobed 

 masses at the sides of the gut, extending as far forward as the base of 

 the pharynx. 



Habitat. — From coarse sand at the bases of Corallina officinalis, 

 Plymouth (F. W. G.). 



34. Plagiostoma pseudomaculatum, n. sp. 



Length 2 mm. Body elongate, pointed behind, the anterior end not 

 distinctly separated off from the rest of the body ; hence it may be 

 distinguished from PI. maculatum, which this species closely resembles 

 in form and in many points of structure. Colour white, a violet patch 

 of reticular pigment between the eyes. Mouth lies beneath the brain. 

 Pharynx very muscular. The genital aperture is ventral, at the base 

 of the tail. The germaria lie right and left behind the pharynx ; 

 behind these again the testes. The vasa deferentia are distinctly 

 swollen before entering the cylindrical muscular penis. 



Habitat. — This species, so far as my experience goes, belongs to a 

 deep-channel fauna of Plymouth, characterised more especially by the 

 presence of various Monotidce, to be presently described. I have 

 found it always associated with Polydora ciliata (Polychseta), which 

 forms mud-tubes in hundreds on the muddy bottom of the Hamoaze. 



This species differs from Plagiostoma ynaculatum in the absence of 

 the red intestine and lateral head-grooves which characterise the 

 latter. 



35. Plagiostoma sagitta (Uljanin, 41). 



Length 1 mm. Body elongate, conical in front, tapering gradually 

 backwards from the middle. The tail not so long as in the preceding 

 species. Colour opaque white with a slight yellowish tinge, due to 

 the contents of the gut. Rhabdites, grouped in clumps, are present 

 over the surface. Pharynx behind the brain, which is transversely 

 elongate, deeply incised anteriorly. Two pairs of eyes are present, 

 placed over the brain ; the hinder pair is the larger, and is markedly 



