BRITISH MARINE TURBELLARIA. 213 



margin is bent upon itself, and produced into an extremely fine, needle 

 like spine, Germaria and vitellaria as in Pr. balticus. A spermotheca 

 is present near the genital pore. 



Habitat. — Dredged off the "New Grounds," Plymouth Sound 

 (F. W. G.). 



C. ALL(EOC(ELA. 



The following definitions are v. Graff's (53), as amended by Bohmig 

 (57, pp. 464-5) : 



Alimentary canal and parenchyma generally sharply separated ; a body- 

 cavity absent in the adult. Nervous and excretory systems present. 

 Testes follicular. Germ- and yolk-glands separate or united, paired ; 

 the latter irregularly lobed, rarely branched. Gonads contained in 

 parenchymatous cavities without a membrana propria. Penis formed 

 by folds of the genital atrium. No conspicuous chitinous copulatory 

 organ. 



Family PLAGIOSTOMIDiE. 



Allceoccela with pharynx variabilis (except Flag, bimaculatum, where it 

 is a pharynx plicatus), the size and position of which is subject to 

 variation. Genital pore single or double ; sometimes combined with 

 the mouth. An otolith absent. 



Sub-family Plagiostomijle. 



Plagiostomidm with a ventral and posterior genital aperture. Mouth 

 anterior. Germaria and vitellaria distinct. 



Genus 17. — Plagiostoma, 0. Schmidt (28), 1852. 

 Without tentacles. 



31. Plagiostoma dioicum (MetschnikofF, 37). PI, XI, fig, 11. 



Length "6 — - 7 mm. Body cylindrical, tapering very slightly in 

 front of the posterior third. Colour yellow-brown, lighter anteriorly 

 and at the sides ; eye pigment reddish brown. The epidermis contains 

 a few small rods and numerous highly refractive vesicles. Bohmig 

 (57, p. 408) has seen these in sections; they are possibly excretory. 



