52 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA 



Gyratrix hermaphroditus Ehrbg. (PI. 4, fig. 5). 



This species appears to be widely distributed. It is about 

 2 mm. in length, is almost transparent and is a rapid and 

 graceful swimmer. It can easily be recognised by the com- 

 paratively long stiletto at the posterior extremity. This weapon, 

 although connected with the male copulatory apparatus, is 

 furnished with a gland which probably secretes a poison of some 

 kind and is used by the animal when attacking its prey. It has 

 a well-marked proboscis, behind which are two eyes. The mouth 

 and pharynx are situated near the middle. As a general rule, 

 only one egg-capsule is present, and this produces one or two 

 embryos. 



The field is almost unworked as regards this country. Von 

 Graff records 110 species of Ehabdocoelida from Germany. As far 

 as the writer can ascertain, only 30 species have been recorded 

 from the British Isles. It is hoped that this short account 

 mav arouse the interest of some of the members of the Quekett 

 Microscopical Club in these interesting animals. 



List of British Species. 



In the following list the descriptions of the species will, unless 

 otherwise stated, be found in Die Silsswasserfauna Deutschlands, 

 Heft. 19. The initials H. W. after the localities denote that the 

 species has been found by the author at those places : 



Sub-order RHABDOCOELA. 



Section Hysterophora. 



Fam. CATENULIDAE. 



Catemila lemnae Ant. Dug. 

 Near Cork (14). 



Stenostomum leucops (Ant. Dug.). 



Common (14) ; Clare Is. (24) ; Staines (H. W.). 



S. unicolor 0. Schm. 

 Clare Is. (24). 



