DESCRIPTIONS OF GENERA AND SPECIES 



391 



the others ; P. houlleti, as I have pointed out, agrees with P. biserialis and P. acystis 

 in this character ; HOKST has described the whole of the setae on the ventral side 

 of the body in Perichaeta as being very large as compared with those on the dorsal side. 

 (3) The presence or absence of the setae on the clitellum is a matter which has 

 been often overlooked ; and yet it offers a very good character for the distinguishing 



Fig 44. 



I 2 3 8 B 7 D 9 IP II 12 13 14 15 IB 17 25 



d. 



e--- 





/\ 



CURVES SHOWING THE NUMBER OF SETAE ON THE ANTERIOR SEGMENTS OF 



CERTAIN PERICHAETA. 



[The segments arc numbered above, the number of setae in tens on the left.] 

 a. P. taprobanae. b. P. dyeri. c. P. sinensis. d. P. barbadensis. 



e. An unidentified species from Hong-Kong. 



f. P. bermtidensis. 



of species ; the degree to which the setae are developed is also important ; in P. tapro- 

 banae, for instance, the setae are present, and to the full number, on all the segments 

 of which the clitellum is composed ; in P. indica we have the opposite extreme ; 

 there are in this species no setae at all upon the clitellum ; this statement, of 

 course, refers to the mature worm ; when the clitellum is undeveloped, the segments, 



