45 



but it is not improbable however that in the future the genus I'roneomenia will be divided into 

 smaller genera. As Proneomenia Weberi and longa show the principal characteristics of the 

 genus Proneomenia (poh'stichous radula, structure of the integument, 2 salivary glands, no 

 gills), a division of this genus should as yet not be recommended. 



What has been noticed in Proneomenia, holds good for Rhopalomenia. Whilst in Rhopalo- 

 menia aglaopheniae and Hisigi the loss of the radula points towards their origin from sj^ecies of 

 Proneomenia, it is much more jirobable that Rhopalomenia indica and debilis are related to a 

 form like Dinomenia. The numerous receptacula seminis of Rhopalomenia indica point towards 

 some relation with Dinomenia verrucosa, just as the rudimentary radula-sac of Rhopalomenia debilis 

 points to a certain relation with Dinomenia, which has a distichous radula. However a relation 

 between Rhopalomenia indica and Proneomenia thulensis is also very well possible. The absence 

 of a radula in Pronomenia and Dinomenia may give rise to forms closely resembling each other 

 both of them with a thick cuticle, pointed spicula in many layers, 2 l(mg .salivary glands, no radula. 



Proparamenia and Paramenia differ considerably in the structure of the integument. A 

 transition-form between the two is not known, but the possibility of such a form is proved In' 

 Cyclomenia, which has a thick cuticle and needle-shaped spicula, but is without [papillae. For 

 the rest Cyclomenia and Dinomenia are related to Paramenia, and show that the integument 

 may develop in the direction of Proneomenia, whilst the radula remains distichous. 



As a consequence of these facts, the relation between the known Xeomeniidae may be 

 established as follows : 



Dinomenia 



Cyclomenia 

 ParaiThopalia 



Priivotia 



Rhopalomenia indica 

 I and debilis 



Proneomenia thulensis 



Strophomenia 



Notomenia(?) 



Rhopalomenia aglaopheniae and Kisigi 



Proneomenia 



Proneomenia Weberi Proneomenia vagans Kow. & M. 

 and longa 



Proparamenia 



Macellomenia 

 ^Paramenia 



Amphimenia 



Stylomenia 



Hemimenia-Neomenia 



Dondersia 



Myzomenia 



Nematomenia 



Echinomenia "Ismenia Lepidomenia. 



