388 OLIGOCHAETA 



Genus PERICHAETA, SCHMARDA. 



Syn. Megascolex, VAILLANT et alii (in part.). 

 Nitocris 

 Amyntas 



Pheretima \ KiNBERG (? in part.). 

 Rhodopis 

 Lampito 

 Perriera, VAILLANT. 



DEFINITION. Perichaetidae with complete circles of setae. Clitellum nearly always 

 limited to three segments. Gizzard in segments VIII, IX, the intervening 

 mesentery being wanting; a pair of caeca nearly always present in segment 

 XXVI. Nephridia difflise ; no penial setae. Spermiducal glands lobate. 



The majority of the species of earthworms which have been described under the 

 names of ' Perichaeta' or 'Megascolex' really belong to the genus Perichaeta as 

 diagnosed above. 



The range of structural variation in the genus Perichaeta is not great. Size alone 

 seems to distinguish a few species ; thus, P. violacea and P. mininia are to be 

 distinguished by their small size, while P. vordermanni and P. mu&ica, especially 

 the latter, are remarkable for their large size ; P. feae and P. longa are also large 

 species. With these exceptions, the measurements of the various species are not 

 apparently widely different. 



The colours during life are known or have been described in too few species l for 

 that to be used as a character of much value. The difficulty of describing colour- 

 differences is also a bar to the use of this character. 



The following points seem to be the principal ones in which the species differ ; 

 the list is drawn up from BOURNE'S remarks upon the subject (4) as well as from my 

 own observations upon a considerable number of species, 

 (i) Number of setae upon the segments. 



(a) Inequalities in size between the setae of different segments or between the 

 setae of different regions of the same segment. 



(3) The presence or absence of setae on the clitellum. 



(4) The number of segments occupied by the clitellum. 



1 Only in P. viridis (SCHMARDA), P. indica, P. morrisi, P. rjij'ii, I', ^lu-nxis, /'. vimatrana (BEDDARD"). 



