AN ATTEMPT TO CLASSIFY EAETHWORMS. 203 



13. Acanthodrilidse. 



14. Perichsetidse. 



15. Plutellidffi. 



16. Pleurochsetidse. 

 ? 17. Moniligastridse. 



He gives the characters of the first eleven of these families^ 

 but does not characterise the remaining six. As will be seen 

 below, I shall split up some of his families, and unite others 

 into one family. 



Rosa^ does this to some extent ; but I have not taken quite 

 the same lines as he has. He retains Claparede's "Terri- 

 colje " for the members of the last nine families, and groups 

 these into six families ; and regards " Terricolse " as of equal 

 value to any of the first eight of Vejdovsky's families. 



Vaillant, in the recently published volume ' Anneles ' 

 (' Suite a Buff'on '), divides the Oligocheeta into two groups : 



(1) N aid in a, including Vejdovsky's first three families ; 



(2) Lumbricina, including the remainder with the excep- 

 tion of Discodrilidse. 



But, as he only deals with the genera and species of earth- 

 worms known up to and including Perrier^s memoir in 1872, 

 his subdivisions are not of that value that we should expect in 

 such a work. 



I. Nomenclature of Certain Organs. 



Before proceeding to the classification which I have to sug- 

 gest, I will make a few remarks on the words and terms 

 employed therein. 



The setae in a large number of worms are arranged, as in 

 the common earthworm, in '' twos.^^ These are nearly always 

 spoken of as '' pairs " by writers on the subject ; but this word 

 seems to me to be ill-chosen : by " pair " we usually under- 

 stand a right and a left organ of a bilaterally symmetrical 

 animal. I suggest, therefore, the word "couple '^ to denote the 



^ Rosa, " Nuova Classificazione dei Tcrricoli," Boll, d. Mus. Zool. ed Auat. 

 Comp.,' tom.iii, 1882. 



