Species of North American OUgochcBta. 397 



like that figured by Leidy, and from its tip to the mouth 

 of the worm measures .3-.4 mm. It is about .03 mm. 

 in diameter at tlie base and tapers shghtly toward the 

 tip. The number of somites in sexually mature specimens 

 is about 30, being- subject to variation. The number in 

 specimens with budding zone in an early stage is 24-30, 

 plus an indefinite number of indistinguishable ones at 

 the posterior end. 



The dorsal set£e agree in number and length with 

 those of Leidy's species. There are three in each bundle, 

 the first ones occurring on II. Those of III are about 

 .7 mm. in length, while those of other somites are .3-. 35 

 mm. In young specimens each of the bundles usually 

 shows the dorsal setae of different lengths, only one 

 having attained the normal length, a second being one 

 half or two thirds as long, and a third quite short. In 

 older and sexually mature specimens they are approxi- 

 mately equal. The dorsal bundles contain only capil- 

 lary setae, but these differ from the ones ordinarily found 

 in naidiform worms in being slightly curved, and in hav- 

 ing minute slender teeth upon the convex side, which give 

 a serrated appearance to the setae (PI. XXXV., Fig. 6). 

 The proximal teeth are about .006 mm. apart, and the 

 serrated condition is most conspicuous near the distal 

 end, the proximal half of the fully developed seta being 

 "without teeth. These serrations seem to be a constant 

 character and are perfectly distinct when examined with 

 high powders, yet they might easily be overlooked, and per- 

 haps escaped Leidy's attention. The ventral setae (PI. 

 XXXV., Fig. 5) are iu bundles of 5-9, though the more 

 usual number is 6-8. They are about .05 mm. in length. 

 Sexually mature specimens have one pair of genital setae 

 on each side of VI iu place of the ordinary ventral setae. 

 These genital setae are bifid at the outer extremity and 

 shaped much like ordinary setae, but are somewhat 

 straighter and about one half longer. 



