14 ZOOLOGISCHE MEDEDEELINGEN — DEEL II. 



In the preceding key the name of Thalenessa was substituted by 

 Euthalenessa, as proposed by Darboux l ) and as has been approved by 

 von Marenzeller 2 ) and Ehlers 3 ) ; for the genus Thalenessa was established 

 by Baird 4 ) in 1868 for Sigalion Edwardsi Kinb., a species which has 

 proved to belong in fact to the genus Sigalion, because the tentacle is 

 absent. It was therefore at variance with the rules of nomenclature, that 

 Mc Intosh afterwards gave that name to a group of Sigalioninae, w i t h a 

 short tentacle. The name of Stenolepis Willey 5 ) has been omitted, while 

 I believe that it cannot be maintained; for in 1905 the English author 

 has united under that name those Leanira-species, that are characterized 

 „by the presence of a long tentaculum impar born upon a ceratophore, 

 which is provided with a pair of spatulate appendages", suggesting that 

 the true jLeamra-species were distinguished „by the presence of a very 

 small tentaculum impar, inserted directly upon the prostomium, not born 

 upon a ceratophore". This suggestion, in my opinion, is not correct, for 

 Ehlers says about Leanira hystricis G ), that the tentacle emerges from 

 the middle of the cephalic lobe and consists of a cylindrical basal joint 

 and slender terminal part ; also Lean, tetragona (Oerst.) 7 ), one of the 

 eldest described species of Leanira, shows a tentacle with conspicuous 

 ceratophore and ctenidia. Therefore I think it not to be permitted to 

 divide the species of Leanira into two groups, on account of the length of 

 the tentacle and the absence or presence of antennal ctenidia. 



Leiden, December 1915. 



1) loc. cit. p. 79. 2) loc. cit. p. 8. 



3) Die bodensâssigen Annelideu der deutschen Tiefsee-Expedition, 1S98 — 99, p. 52. 



4) Journal Linnean Society, Zoology, Vol. IX, 1868, p 34. 



5) loc. cit. p. 259. 



6) ZeiUchr. t. Wissensch. Zoologie, Bd. XXV, 1874, p. 35, PI. II, figs. 5—11. 



7) Malmgren, Nord. Hafs^annulater, p. 88, pi. XI, fig. 14. 



