OLIGOCH-^TA. 267 



the term " Hakenborsten," which Michaelsen applies to the shorter 

 dorsal setae of A. palustris, can be used for those of the present form. 

 The definition of a " Hakenborste " is " eine verhaltnismassig kurze 



S-formig gebogene Borste ," (Michaelsen, 5) ; and it is 



evident that the dorsal setae of the present form are not, as are the 

 ventral setae (to which the term" Hakenborsten ' ' is properly applied) , 

 curved like the letter S. The dorsal setae of the form here described 

 are more properly termed needle -setae, since " eine Nadelborste 

 entsteht aus der Hakenborste, wenn diese ihre S-formige Kriimmung 

 aufgiebt " (ib. id.). The point is of some importance, as owing to 

 the degree of variability in the development and possibly in the 

 number of the gills in this and the allied genus Dero, the setae may 

 probably be found to afford a more rehable means of discrimination 

 of the several species (c/. Michaelsen, 6). 



Hesperodrilus ZEYLAisricus, sp. nov. 

 (Plate I., Fig. 6.) 



A single specimen, found crawling on the under surface of a stone 

 aken from a streamlet running down the bank of the lake in very 

 marshy ground, Nuwara Eliya, Ceylon, 6,000 feet. 



The specimen was curled up, and damaged (nearly severed) at one 

 place near the posterior end ; many of the dorsal setae had also been 

 broken off. The length wa,s estimated at 8 mm. ; breadth, maximum 

 • 6 mm. ; segments 34 with a small undifferentiated region posteriorly. 

 Prostomium short, bluntly conical ; the length from tip of pros- 

 tomium to mouth is about equal to the length of a body -segment. 

 Clittellum 1/5 XII.-XIII. = 11/5. 



The dorsal setas begin in segment III., and are all capillary ; they 

 vary in thickness, some being much stouter than others ; this 

 difference exists in many cases between the setae of the same bundle. 

 The largest number in a bundle was five ; four were counted not 

 infrequently. In length, the longest (-58 mm.) are about equal to 

 the diameter of the body. 



The ventral setae are as a rule two per bundle ; of the two, one is 

 a simple hook, while the other is forked at its free end (fig. 6) ; 

 both have the usual double curve. The forked setae are 118-123 fx 

 long ; the prong on the outside of the curve is much the smaller, 

 being only about half as long, and one-third as thick at its base, as 

 the other ; the nodulus is sUght, and is markedly distal to the 

 middle of the shaft (distal : proximal : : 45 : 73 or 47 : 76) ; the shaft 

 is stout — 6 • 3 [). broad — considerably stouter than that of the singly 

 pointed setae. 



The singly pointed setae are about the same length as the forked 

 setae ; the curves of the shaft are slightly less pronounced ; there is 

 no nodulus ; and the shaft , though varying in thickness in different 

 bundles, is considerably thinner {e.g., 3*4^) than tliat of the doubly 

 pointed setae. 



