Two New Oligochoeta from Illinois. 143 



A few points of difference seem to sharply distinguish 

 the two forms. The worms from Illinois are the larger, 

 and have a length, when moderately extended, of 18 to 

 20 cm. I have alcoholic specimens fixed after being 

 anaesthetized, which, without being unnaturally extended, 

 are over 20 cm. in length, and average .26 cm. in diameter. 



The arrangement of setae in the two forms differs 

 chiefly in the position of the outer couples, which are in 

 the dorsal half in the new form, instead of in the ventral 

 half as in 8. tamesis* Sections have a quadrangular 

 outline, with a couple of setae at each angle, tlie arrange- 

 ment being similar to that in Criodrilus. The distance 

 between the outer or dorsal couples is one and a fourth 

 times that between the inner or ventral couples in the 

 region posterior to the clitellum, and about one and a 

 half times as great in the region anterior to the clitellum. 

 The distance between the outer couple and the inner 

 couple of the same side is slightly greater than that 

 between the two inner couples. The setae of a couple 

 are quite closely approximated. As in S. tamesis, the 

 outer setae are missing in the region where the clitellum 

 is fully developed. Specimens taken late in the season 

 have setae in this region. 



The spermathecal pores are in line with the setae of 

 the outer couple, as in S. tamesis, but in consequence of 

 the dorsal position of that couple in the new form, the 

 pores are upon the dorsal half of the animal. 



The form of the region of the clitellum during repro- 

 ductive activity is different from that at other seasons 

 and from that figured for 8. tamesis. At that season 

 the ventral part of the clitellar region, including the 

 ventral i-etae and the tubercula pubertatis, is slightly con- 

 cave downward, and forms two very conspicuous ridges or 

 actual folds where it meets the lateral walls. This 

 concave appearance, though intensified by the action of 

 alcohol in hardening, is not produced by it, but i« 

 present in the living worm. 



♦Benham. loc. cit.. PI. XIX., Fig. 8. 



