DESCRIPTIONS OF GENERA AND SPECIES 363 



Perriera (for P. biaerialis). These subgenera are indicated in a table which is 

 slightly altered from that of KINBERG. 



In 1871 PERKIER added a new genus Perionyx to Perichaeta, considering it possible, 

 however, that this genus might later be regarded as not really distinct. The principal 

 character in which it differs from Perichaeta is in the presence of paired nephridia 

 (' la nettete' de ses organes segmentaires '), the inclusion of the male pores in a 

 circumscribed ventral area, the position of the spermathecae, and the extent of 

 the clitellum. 



The two first characters alone distinguish the genus as now defined. When PERKIER 

 wrote of the position of the spermathecae as serving to distinguish the genus he must 

 have meant the structure of these pouches, i. e. the absence of a diverticulum. There 

 is nothing remarkable in their position. This genus has been accepted by all subse- 

 quent writers except VAILLANT, and is admitted here. In 1881 I added a new genus 

 Pleurochaeta ; the identity of this form with TEMPLETON'S Megascolex, suspected by 

 VEJDOVSKY (24), was later proved by myself (5). 



Below I have something to say with reference to the confusion which has been 

 made with the genera Megascolex and Perichaeta; here I am concerned with the 

 genera of Perichaetidae alone. The distinction between Perichaeta and Megascolex 

 was first pointed out by SCHMARDA, who introduced the latter name ; his distinctions, 

 however, were based upon a misunderstanding of TEMPLETON'S description of Mega- 

 scolex ; indeed he re-described M. coeruleus as P. leucocyda. BAIRD (1) denied that 

 there was any distinction between any two such genera ; but his opinion is rendered 

 of little value by the fact that he paid no attention to internal characters, and for 

 the matter of that but little to external characters also. 



In 1883 I pointed out that two genera, Megascolex and Perichaeta, might be 

 distinguished as follows: 



PERICHAETA. 



(1) Ring of setae upon each segment discontinuous at one or more points. 



(2) Clitellum occupying more or fewer segments of the body than three. 



MEGASCOLEX. 



(1) Ring of setae continuous. 



(2) Clitellum occupying segments xiv-xvi. 



It will be observed that I have here defined as Perichaeta the worms now referred 

 to Megascolex and vice versa. This was on the strength of BAIRD'S statement that 

 Megascolex and Perichaeta were the same. I should, however, in that case have 

 allowed the name Perichaeta to be dropped, and have introduced a new name. 



3 A 2 



