804 PROCEEDINGS OF THE ACADEMY OF [DeC, 



till the posterior end is approached. Somites II and III are simple; 

 IV is biannulate, with the furrow just behind the setse and consequently- 

 nearer to the posterior margin; V has a median setigerous annulus 

 partially cut off from the larger annulus. The remaining preclitellial 

 segments are conspicuously triannulate, the middle or setigerous annu- 

 lus being the narrowest but most prominent. Occasionally the first 

 annulus is again subdivided into two. When the clitellum is present, 

 as in most of the specimens, the segments of this region are smooth 

 and undivided, dorsally at least, but in immature worms the annula- 

 tion appears here also. In all but the most posterior of the postclitellial 

 somites also the triannular structure is apparent, but is generally in- 

 conspicuous except in the more anterior ones or those strongly con- 

 tracted. 



The usual four pairs of setse are present on all somites except the 

 peristomium, a few preanal, and XIX, the latter of which lacks the 

 ventral pairs only. All are strictly paired and strongly ventral in 

 position, but the intervening spaces vary somewhat. On XVI the 

 setal formula is a-b < j a-a, a-a= 2 J c-d, a-b = %c-d, b-c < a-a, d-d = 

 about f semi-circumference. Ordinary seta? stout, sigmoid, blunt- 

 pointed, thickened distad of middle, the outer end slightly sculptured 

 with a reticulum of fine lines giving to the setse an appearance of being 

 covered with delicate scales. Spermathecal copulatory setse (the 

 ventral ones on VII, VIII and IX) similar but with much bolder sculp- 

 turing and apparently unaccompanied by special glands. Penial setse 

 (the ventral ones on XVIII and XX) capillary, tapering, somewhat 

 thickened within the body-walls, with slight sinuous curvatures, 

 especially near the end, which may be slightly hooked. They are 

 about twice as long, or somewhat more, than the ordinary setse, and 

 only -I" to 1^ as thick. Near the end is a sculptured region marked with 

 close transverse lines appearing as fine notches on the profiles, but the 

 end itself for a considerable distance is smooth or longitudinally 

 striated. 



Dorsal pores begin at ^ or usually j^-^ and are conspicuous. The 

 position of the nephridiopores is remarkable in being widely removed 

 from the dorsalmost seta; while the former are situated at approxi- 

 mately the two ends of the transverse diameter of the body the latter 

 are fully 15° to 30° below these points. Successive nephridiopores 

 are usually alternately at a little higher and lower level and are on the 

 extreme anterior borders of the somites — almost in the furrows — the 

 first on III. Spermathecal pores are less easily found. They occur 

 in line with seta a on the anterior part of somites VII, VIII and LX, 

 and are consequently presetal and postseptal. 



