BRITISH MARINE TURBELLARIA. 441 



muscular. The otolith has a distinct central portion, and is 

 radially striated. The two eyes are large, and provided each 

 with a lens. The common genital pore lies at the hinder 

 end of the body. It leads into a ciliated, muscular, narrow 

 atrium, which is an invagination of the hinder extremity. 

 Testes rounded, scattered. Vesicula seminalis spherical, 

 opening into the pyriform muscular penis enclosed in its sheath. 

 These organs lie at the front end of the genital atrium. 

 The spermatozoa when mature are broad and thick, taper- 

 ing at either end, the head filament shorter than the tail. 

 Ova occur in two lateral rows, sometimes those of one side 

 being more developed than those of the other (v. Graflf). 



Habitat. — This active yellow form is not uncommon 

 between tide-marks in Plymouth Sound (F. W. G.). This is, 

 I believe, the first record of its occurrence north of the 

 Mediterranean. 



Distribution. — Trieste, Naples, Messina (v. GraflF), Lesina 

 (Schmidt, 28), Sebastopol (Uljanin, 41). 



Genus 2. — Monoporus, v. Graff (56) 

 (= Proporus, Schmidt, 28). 



Proporidse with spermotheca. 



2. Monoporus rubropunctatus (O. Schmidt, 28). 



Length 1 mm. Body ellipsoidal with rounded extremi- 

 ties. Colour white, the central parenchyma brown, owing 

 to the presence of coloured vacuoles and food-particles. The 

 epidermis contains clavate rhabdites, the thickened outer 

 ends of which project beyond the surface. The mouth is 

 mid-ventral, leading into a very short simple pharynx; the 

 " terminal mouth " of earlier descriptions being, according to 

 V. Graff (56, p. 57), the opening of the '^frontal organ." The 

 eyes lie right and left close to the anterior end. They are 

 placed in the epidermis, and consist of polygonal pigment 

 masses of a brilliant carmine colour. In his recent accounts 



VOL. XXXIV, PART IV. — NEW SEE. G Q 



