THE OLIGOCH^TA OF NATAL AND ZULULAND. 457 



23 a. The median ventral distance between the innei-most 

 ventral setaj diminishes distinctly towards the copula- 

 tory walls. Copulatory walls extend from the fifteenth 

 to the eighteenth segment. Sexnal setae about 2|-3 

 mm. long, and at the proximal end about 60 fi thick, 

 distinctly Isent at the thinner proximal end, the re- 

 maindei" nearly straight except at the distal end. where 

 it is slightly bent, thickened and broadened to a 

 breadth of about 80 ju. One of the broad sides convex, 

 the other hardly convex. Tip rather blunt, or two tips 

 with a concave edge between them ; external ornamenta- 

 tion consists of somewhat irregular, rather densely 

 crowded annulations, the distal borders of which are a 

 little prominent ; they are scale-like and covered by 

 dense rows of very minute teeth. 



Microchfetus natalensis (Kinb.) 

 23 b. The median ventral distance between the innermost 

 ventral seta3 does not diminish distinctly towards the 

 copulatory walls. Copulatory walls stretch over seg- 

 ments 16-20, and are prominent laterally. Sexual setae 

 l'75-2-5 mm. long, and proximally 80-90 ft thick, slightly 

 bent into the form of an S ; external ornamentation 

 consists of more or less oblique annulations, the scaly 

 distal margins of which are irregularly toothed or 

 pronged. . . Microchsetiis papillatus Benh. 



a. Clitellum extends from the tenth to the twenty- 

 ninth or thirtieth segment. Copiilatory cushions 

 - indistinct ; distal tip of the sexual setae sharpened 

 to form a triangular pyi-amid with deeply carved 

 sides. . . . . f. typicus 



j8. Clitellum extends from the twelfth to the twenty- 

 fourth segment. Distinct copulatory cushions 

 stretch over segments 17-20. Distal part of sexual 

 seta; generally end in two thick, short teeth, which 

 are joined by a web-like membrane nearly as 

 thick as the teeth. . . var. caementerii >i. -yar. 



24 a. Setae strictly paired. Clitellum l)egins at the twenty- 

 seventh or twenty-eighth segment, and reaches as far 

 as the thirty-fourth or thirty-fifth. Distinct copula- 

 tory wall at segments 31-33. Four pairs of sperm-sacs 

 in segments 9-12. Spermathecae present. 



Helodrilus caliginosus (Sav.) f. trapezoides (Dug.) 

 2-4 b. Setae widely paired. Clitellum extends from the twenty- 

 sixth to the thirty-second segment. Copulatory walls 



