4 TURBELLARIA. 



ft Eyes two. 

 C. Dalyellia. Mouth terminal. 



7. Derostoma. Mouth ventral, anterior. 



8. Mesostoma. Mouth ventral, subcentral. 



Suborder II. Teretularia. 



The body cavernous, linear-elongate, subcylindrical or compressed, 

 very contractile, sometimes breaking spontaneously into pieces, the 

 surface even and smooth, or rarely wrinkled : head more or less 

 distinct, the mouth a simple terminal or subterminal pore, with a 

 very long included proboscis : intestine undivided, laid in the visceral 

 cavity, with the vent situated well forwards, or posterior and ter- 

 minal ? There is a larger aperture below the head which leads to 

 the common cavity. 



* Acephalous: the anterior end plain. 



12. Astemma. Eyeless. 



13. Cephalotrix. Eyes two, parallel. 



14. Tetr astemma. Eyes four, in a square. 



** Acephalous, with a furrow on each side of the front. 

 20. Serpentaria. Body flat, elongate, uniformly coloured, fragile. 

 19. Meckelia. Body linear-elongate, fragile, with paler annulations. 



*** Cephalous, the head indistinct, multocular, and mostly with a shallow 

 furrow on each side. 



15. Borlasia. Eyes in a submarginal series : oesophagus simple. 



16. Omatoplea. Eyes clustered, irregular: the oesophagus with 



horny stylettes. 



17. Stylus. Anal extremity armed with a long style. 



**** Ophiocephalous, with lateral furrows. 



18. Lineus. 



