BRITISH MARINE TURBELLARIA. 455 



The yolk-glands are lateral, uniting behind the brain. A 

 small muscular sac placed behind the penis appears to be a 

 receptaculum granulorum. 



Habitat. — Two specimens among littoral weeds, Plymouth 

 (F.W. G.). 



Distribution. — West coast of Greenland (Levinsen). 



Levinsen's description (according to v. Graff) left this form 

 indeterminate. The two . pyriform bodies that he called 

 " Samenblasen/^ and which v. Graff suggested might be local 

 swellings of the vasa deferentia, I take to be the true testes. 

 They have all the structure of such an organ, but occupy a 

 more posterior position than usual. The ova did not appear to 

 Levinsen to be distinguishable into two fairly distinct ovaries 

 as in my specimens. 



Subfamily Byrsophlebin^. 



Mesostomidse with two genital apertures, the 

 male in front of the female. Germarium single. 

 Vitellaria distinct. Accessory organs absent or 

 present. Testes small, rounded. 



Genus 8. — Byrsophlebs, Jensen (49). 

 (With the diagnosis of the subfamily.) 



15. Byrsophlebs Graffi, Jensen. 



Length -45 mm. Body cylindrical, tapering gradually 

 posteriorly. Colourless, the gut brownish-yellow. Pharynx 

 central, male genital aperture immediately behind it, 

 female aperture close to the hinder end. Penis composed of 

 a proximal cylindrical portion, strengthened by spiral and 

 longitudinal muscles, and a distal chitinous funnel-shaped duct. 

 The terminal aperture of this duct is provided with a short 

 triangular projection on one side. Opening through the 

 female genital aperture is a receptaculum seminis placed 

 at the base of the ovary, and a muscular bursa copulatrix 



