474 F. W. GAMBLE. 



34. Plagiostoma pseudomaculatum, n. sp. 



Length 2 ram. Body elongate, pointed behind, the 

 anterior end not distinctly separated off from the rest of the 

 body ; hence it may be distinguished from Pl.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 Monotidse, to be 

 presently described. I have found it always associated with 

 Polydora ciliata (Polychgeta), which forms mud-tubes in 

 hundreds on the muddy bottom of the Hamoaze. 



This species differs from Plagiostoma maculatum 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 reniform. 

 Genital aperture at the base of the tail. The vesicula semi- 

 nalis contains spermatozoa, which have a central rib, bearing 

 broad triangular lateral membranes, exactly similar to the 

 spermatozoa of Plagiostoma maculatum. Contrary to 



