Illinois Oligochaeta. 453 



is, as in many Tubificida, the principal respiratory region. 

 Non-retractile sense papillae similar to those described for 

 Embolocephalus, Spirosperma, and a few other Tubificidtz, are 

 present in this species. They are arranged in two rows on 

 each somite, one row coinciding with that of the seta; bundles 

 of the somite, and the other one being usually in the plane 

 of the septum (PL XXXIX., Fig. 1). A few papilla repre- 

 senting a third, very incomplete, row are often present. 



When a specimen is examined with a lens, one is strongly 

 reminded of some of the marine annelids by the dense clusters 

 of elongated sets in the dorsal bundles. The dorsal setae are 

 of two kinds ; long capilliform set*, often .5 mm. in length, 

 and' palmate or comb-like setae .16 to .18 mm. in length 

 (PI. XXXIX., Fig. 2, c, d.). In the anterior bundles capilli- 

 form setae vary in number from three to fourteen per bundle. 

 Throughout most of the remainder of the body the number 

 is but one to three per bundle, while the last ten to twenty 

 somites usually have no dorsal seta? whatever. The palmate 

 setae are regularly found in only a few anterior somites, 

 where the number varies from one to five per bundle. In the 

 dorsal bundles of the greater part of the body back of the 

 first ten or twelve somites, palmate setae are usually lacking, 

 though occasionally one such may be found in one or more 

 bundles posterior to the middle of the worm. The relative 

 number of capilliform setae and palmate setae per bundle is 

 extremely variable. Some individuals have setae of the two 

 kinds in equal numbers, while others having a relatively large 

 number of capilliform setae have only one to three palmate 

 setae per bundle. Ventral setae, usually two in each bundle, 

 are present in all the somites except the first, eleventh, and 

 last. They are sigmoid, uncinate, and slightly enlarged at a 

 distance from the distal end about equal to one third the 

 length of the setae. The ventral seta? of the anterior region 

 are longer and less strongly curved than those of the posterior 

 part of the body (PI. XXXIX., Fig. 2, a, b). 



There is no well-developed clitellum on any of the speci- 

 mens in our collection, none of which seem to lie at the 

 height of sexual activity, but in a few individuals the 



