THE GENERA OF NEMERTEANS. 195 



Prosorhochmus , Keferstein .... 1868. 

 Drepanophorus , Hubrecht .... 1874. 

 Avenardia, Giard 1878. 



It is clear that for an order of worms , which is yet 

 so imperfectly known as the Nemerteans, this extraordi- 

 nary large number of genera must contain many synonyms. 

 Authors who failed to find well marked characters , by which 

 to distinguish the species of these worms (which moreover 

 showed such a protean variability in their external appearance) 

 highly overvalued any small structural difference which 

 happened to be common to two or more species and im- 

 mediately founded a generic division on so insufficient a 

 basis. The short and incomplete description of many of 

 the genera was further one of the causes which led to 

 unnecessary multiplication of their number, whereas the fact 

 that in many cases no account whatever was taken of the 

 internal anatomical characters, when establishing a new 

 genus, gave rise to a considerable confusion, which it will 

 be difficult to get rid of gradually. 



If we take the three naturalists , whose researches have 

 most contributed to our knowledge of the Nemertini in 

 the last thirty years : Quatrefages , Keferstein and Mac-Intosh 

 we find different genera adopted by each of them and — 

 what is more embarassing yet — a different scope given 

 to the same generical name, in consequence of which 

 Keferstein for instance employs the name Borlasia for 

 worms belonging to the great subdivision of armed Ne- 

 merteans , whereas Mac-Intosh , more strictly adhering to 

 Okens original intention, applies it to an unarmed species. 



Quatrefages who examined atlantic as well as mediter- 

 ranean forms (Annales des Sciences Naturelles Vol. VI 

 1846) admits the six genera Valencinia , Borlasia , Nemer- 

 tes , Folia , Cerebratulus and Oerstedia. Keferstein (Zeitschr. 

 f. Wiss. Zoölogie, Bd. XII) adopts M. Schulze's suborders 

 of armed (Nemertinea enopla) and unarmed Nemerteans 

 (Nemertinea anopla) and establishes three families on charac- 



Notes froni the Leyden IMviseurn. 



