BRITISH MARINE TURBELLARIA. 219 



Distribution. — Bergen (Jensen). 



30. ? Plagiostoma siphonophorum (0, Schmidt, 28). 



Length -9 mm. Body elongate, truncate in front with rounded 

 angles, tapering posteriorly. Along the mid-dorsal line is a narrow 

 band of reticular black pigment, which expands laterally behind the 

 eyes and extends between and beyond them anteriorly. Bohmig has 

 shown (57, pp. 208-9) that this pigment is present in the gut-cells 

 and not in the parenchyma. The mouth lies beneath the brain. The 

 pharynx, when extended through the mouth, is narrow, cylindrical, 

 expanded slightly at the distal end. My observations on the genital 

 organs are incomplete. The penis is pyriform, armed at its base with 

 small chitinous spines. 



Habitat.— In 15 to 18 fms., Plymouth Sound (F. W. G.). 



Distribution. — Lesina (Schmidt), Trieste (v. Graff, Bohmig). 



As ripe sperm was not seen, this species remains doubtful. But 

 other characters agree with PI. siphonophorum, so I refer my specimen 

 to this form. 



40. Plagiostoma Girardi (Schmidt, 32). 



Length 1*75 — 2 mm. Southern examples range up to 3 mm. Body 

 slightly depressed, rounded in front, tapering behind, broadest in the 

 middle. v. Graff's figure ('Monogr.,' pi. xviii, fig. 12) does not 

 represent the form well, whereas, as Bohmig has remarked, the figure 

 of PI. ochroleucum would do so. Colour white. Movements sluggish. 

 Rhabdites abundant over the surface. Pharynx small, opening through 

 the mouth behind the brain. Eyes two, reniform, with lenses. 

 According to Bohmig (57, p. 355), the "ciliated furrow" forms a 

 transverse groove in front of the mouth, and does not correspond to a 

 slight constriction which occurs behind the eyes. For the genital 

 organs the accounts of v. Graff and Bohmig may be consulted. The 

 spermatozoa consist of a midrib, bearing broad triangular hyaline 

 membrane, and terminating in a short anterior and a longer posterior 

 flagellum. 



Habitat. — Not uncommon 6—15 fms., Plymouth Sound (F. W. G.) 



