BRITISH MARINE TURBELLARIA. 521 



II. TRICLADIDA. 



A single (rarely double) genital aperture behind the mouth. 

 Pharynx central or post-central . Family Planariidae. 



a. Penis directed dorso-ventrally. Uterus opens into 



genital atrium. Head truncate. Eyes wide apart 



Genus Gunda. 

 Species : — G. ulvce (the angles of the anterior margin 

 produced into " lappets^'). 



b. Head produced in the centre. Eyes approximated 



Genus Fovia. 

 Species : — F. affinis (pharynx behind the middle). 



III. POLYCLADIDA. 

 Section A. — Acotylea. 



1. Dorsal contractile tentacles present. Tentacular, cephalic, 

 and marginal groups of eyes . . Family PlanoceridsB. 



a. Body leaf-like. Marginal eyes absent 



Genus Planoceba. 

 Species : — PI. folium (tentacles placed behind com- 

 mencement of second quarter of length ; body 

 yellow-brown). 



b. Body distinctly enlarged in front. Tentacles placed 



well apart at end of first fifth of the body. 



Genus Stylochoplana. 

 Species : — St. maculata (two genital apertures). 



2. Mouth subcentral. Main-gut extending in front of 

 (rarely behind) the pharyngeal region. Tentacles absent 



Family Leptoplanidge. 

 a. Body slightly enlarged in front. Marginal eyes 

 absent . . . Genus Leptoplana. 



Species: — L. tremellaris (a '^ sucker '^ present be- 

 tween the male and female genital pores). L. 

 Mertensii and L. atomata (doubtful species, see 

 pp. 501-2). 



VOL. XXXIV, PAET IV. NEW SBR. M M 



