BRITISH MARINE TURBELLARIA. 235 



deeper, the usual gliding ciliary movement is adopted. The hinder 

 part of the body is kept on the substratum, while the anterior 

 extremity is raised up and constantly extended and retracted, the 

 body as a whole partaking of the steady forward movement.* 



Habitat. — Among algse, Firth of Forth (Dalyell) ; Plymouth 

 (F. W. G.). 



Distribution. — Coasts of Denmark, Norway, and Sweden. 



Sub-order 3.-P0LYCLADIDA. 



A. ACOTYLEA. 



Family PLANOCEPJDiF. 



* Mouth and pharynx subcentral. Main-gut rarely extends in front of or 

 behind the pharyngeal sheath. Dorsal tentacles present. Eyes occur 

 (1) on or round the bases of the tentacles • (2) as a double cephalic 

 group ; (3) on the body margin. Development usually direct. 



Genus 27. — Planocera, de Blainville,t 1826. 

 Body broad, leaf-like. Tentacles tapering, contracting into temporary 

 pits. Brain and tentacles lie at the beginning of the second fourth of 

 the body. Marginal eyes absent. Pharynx at rest lies completely 

 folded in its sheath. Two genital apertures some distance from the 

 hinder end. 



60. Planocera folium (Grube). 



1840. Stylochus folium, Grube (14). 



1844. Planocera folium, Oersted (16). 

 1856. „ „ Johnston (38). 



1884. „ „ Lang (54). 



*Bergendal ("Studien ii. nordischen Turbellarien," ' Of vers af Kongl. 

 Vetensk-Akad. Ftirhandlingar,' 1890, No. 6) lias described a species 

 apparently synonymous with the present one, in which the uterus has a 

 separate external opening. He defines a new genus, Uteriporus, containing 

 the single species U, vulgaris, Berg. An accident prevented a re-examination 

 of my specimen. 



* The definitions of families and genera of Polyclads are taken from 

 Lang (54). 



tde Blainville, ■ Dictionnaire des Sciences naturelles,' art. "Planaire," 

 t. xli, 1826. 



