BRITISH MARINE TURBELLARIA. 255 



a. Epidermis without pigment : PL Girardi (colour- 

 less, 2 reniform eyes). PL siphonophorum (with median 

 longitudinal band of black reticular pigment). PL pseu- 

 domaculatum (violet pigment between the eyes, without 

 distinct lateral grooves). PL vittatum (pigment variable, 

 usually in the form of three transverse bands). 



/3. Epidermis pigmented : PL sulphureum (epidermis 

 with yellow rods). PL Koreni (transverse band of 

 parenchymatous pigment). PL caudatum (rhabdites 

 few, head marked off by lateral grooves). 

 b. With two tentacles at the anterior end - Genus Vorticeros. 

 Species: — V. auriculatum (violet reticular pigment over the 

 greater part of dorsal surface), V. luteum (pigment uni- 

 formly yellow). 

 II. A single posteriorly-placed genital aperture. Two germaria 

 and two distinct vitellaria. Pharynx directed backwards. 



Sub-family Allostominse. 



a. Without a circular ciliated groove on the head 



Genus Enterostoma. 

 Species : — E. austriacum (four eyes ; pigment in rounded 

 yellow masses). E. fingalianum (pigment absent, colour 

 due to food). E. caecum (eyes absent). 



b. With a circular ciliated groove at the level of the brain 



Genus Allostoma. 

 Species .•— .4. pallidum (adults 2 — 3 mm. long • granular 

 mucus-rods [pseudo-rhabdites] in the epidermis). 

 III. Circular ciliated groove on the head. Oral and genital aper- 

 tures combined. A pair of germ-yolk-glands present. 



Sub-family CylindrostominsB. 



a. With characters of sub-family - Genus Cylindrostoma. 

 Species : — Oyl. quadrioculatum (pharynx directed forwards ; 



body colourless). Cyl. inerme (epidermis yellow, containing 

 rhabdites but no " calcareous bodies ;" spermotheca absent). 

 Cyl. elongatum (pharynx directed backwards ; four eyes 

 present). 



b. Pharynx directed backwards, the penis forwards. Spermo- 



theca opens into genital atrium. - Genus Monoophoruh. 



