32 A ren icolidae 



favour of the recognition of the differences between the caudate and 

 ecaudate species. The latter differ from the former in their brain 

 and prostomium, in the absence of tail, and in the mode of branching 

 of their gills, but the two ecaudate species diverge very sharply from 

 each other in the number of their nephridia and the nature of their 

 reproductive organs ; in regard to the last-named character especially 

 the differences between A. branchialis and A. ccaudata are as great 

 as between the latter and any caudate species. The opinion of 

 the writer is that the caudate and ecaudate species present such 

 a number of common characters as to warrant their inclusion in a 

 single genus, and that the differences presented by the ecaudate 

 species would be sufficiently recognised by regarding them as of 

 sub-generic importance. It is therefore proposed to maintain all the 

 species in the genus Arenicola. 



Prof. Fauvel has merged Brancliiomaldane with Arenicola, but, 

 for reasons set forth in another part of this volume (p. 155), the writer 

 does not consider this advisable, and therefore maintains the two 

 genera. 



Quatref ages' genus Ckorizobranchus was based on his interpreta- 

 tion of a badly executed figure of " Lumbricus marinus," given by 

 Delle Chiaje in 1825, in which the branchiferous segments are 

 shown separated by abranchiate ones. There can be no doubt that 

 this figure was intended by Delle Chiaje to represent a specimen of 

 Arenicola, for in 1841 he himself cited the figure among the synonyms 

 of A. piscatorum. This new genus, being established on an obviously 

 defective basis, as Claparede soon pointed out, was not recognised by 

 any subsequent writer. 



The genus Clymenides (see p. 75), as defined in the single species 

 sulpliurea of its author, Claparede, is merged with Arenicola because 

 the worm described under this name was almost certainly a post- 

 larval stage of A. marina. The examples of C. sulfur cus described 

 by Prof. Mesuil were undoubtedly young stages of A. marina, and 

 his two new species C. ecaudatus and incertus have been proved to 

 be young phases of A. ecaudata and Branchiomaldane vincenti 

 respectively. 



A GENERAL ACCOUNT OF THE GENUS ARENICOLA. 



The following account of the genus Arenicola relates to the 

 external features, and to those internal organs which are used as 

 factors in diagnosis in the subsequent part of this Catalogue. 



