59 
CLASSIFICATION. 
In order to fix the place of Proneomenia in the system and to 
determine the relative affinities of the genera, that compose the 
class of the AmPHInEURA, the investigations recorded in the fore- 
going pages offer numerous data, which may here be shortly recalled 
to mind, without giving a more elaborate recapitulation. 
Proneomenia is very closely allied to the two other genera of 
the Solenogastres, Neomenia and Chaetoderma : 
1) by its external appearance ; 
2) by the calcareous spicules in its integument; 
3) by its ventral groove; 
4) by the general outlines of its generative apparatus and the 
discharge of the genital products into the pericardium and 
from thence outwards; 
5) by the general outlines of the eirculatory apparatus; 
The affinity to Neomenia is more intimate yet: 
1) by the presence of a double apparatus, perhaps comparable 
to a byssus-gland, close to the posterior extremity ; 
2) by the presence of a ciliated foot inside the ventral groove; 
3) by the arrangement of the nervous system and the presence 
of pedal commissures ; 
4) by the general structure of the digestive apparatus; 
5) by the shape of the genital gland; 
6) by the posterior coalescence of the two tubes, that will even- 
tually have to be regarded as renal organs. 
On the contrary Proneomenia differs from Neomenia : 
1) by the presence of a radula!) (also found in Ch«etoderma) ; 
1) When we keep in view the close relationship which obtains between 
these two genera, I feel convinced that a point of difference of so primary 
importance can only be explained by the supposition that the direct ancest- 
ors of Neomenia were similarly possessed of a radula but that it has there be- 
come degenerate and lost. Althoush very small in Proneomenia it is far too 
complicated in structure to represent a first step in radular development and 
the diminutive size is again confirmatory of the tendency towards degenera- 
tion which I hold it to have in this genus. 
