TWO NKW BRITISH NEMERTEANS. 56l 



(5) The peculiar arrangement of the median dorsal nerve 

 noted above only occurs in Oxypolia. 



Oxypolia also shows affinities Avith Parapol ia, though 

 the absence of a head gland and the single excretory pore 

 readily distinguish this genus from it. With regard to the 

 relative positions of the six genera in the genealogical tree, it 

 seems probable that the sis genera fall into at least two 

 groups. 



On the one hand, the American genera Zygeupolia and 

 Parapolia stand together somewhat apart from the rest. 

 Three of the features which bring them together — i. e. the 

 absence of a specialised gelatinous connective layer in the 

 cutis, the absence of peculiar head glands, and the presence 

 of but a single excretory poi-e — seem at the same time to point 

 to their more primitive nature if we accept Burger's view 

 that the group is derived from a Carinella-like form. This 

 view is emphasised by the presence of a side organ in 

 Zygeupolia, an organ only found elsewhere in Carinella 

 and the primitive Lineid Micrella. Again, the three genera 

 Eupolia, Valeiicinia, and Oxypolia form a group cha 

 racterised by the presence of peculiar head glands, the thick 

 gelatinous cutis layer (except in Valencinia), and an ex- 

 cretory system with many ducts. Of the position of Poli- 

 opsis it is impossible to speak while so many points in its 

 anatomy remain unknown. 



Summary. 



1. Description of two new genera of Heteronemerteans 

 belonging to the families Eupoliidaj and Lineidae, viz. Oxy- 

 polia and Micrella. 



2. Micrella rufa is the most primitive member of the 

 Lineidi«, showing great resemblance to the Carinellidaj, more 

 especially in its excretory system and in the presence of a side 

 organ. 



3. The structure of the caudal appendage in Micrella 

 rufa differs from that of any other Heteronemertean yet 



