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AR.T. III. — Descriptions of some American Annelida ahranchia. 

 By Joseph Leidy, M. D. 



The worms of America, terrestrial and aquatic, have as yet received but little 

 attention from our naturalists. The following descriptions have been taken from 

 notes which have been in possession of the author for many months, and when leisure 

 permits, some others will be presented. 



Nais, Muller* — Opsonais, Gervais.-\ Body filiform, furnished with two rows of 

 podal spines, and lateral setse ; no terminal appendages. Eyes two, placed upon the 

 oral segment. — Leidy. 



1. Nais GRACILIS. PL 2, fig. 1. — Body whitish, linear, divided into fifty 

 articulations, every one of which is provided inferiorly, on each side, with a set of 

 four retractile podal spines slightly hooked at their free extremity. Articulations 

 posterior to the fifth, excepting the two last, furnished on each side with a single 

 long delicate seta, which are pretty uniform in length except the posterior five whicti 

 gradually decrease to the last. Fifth articulation furnished with three setse on each 

 side nearly twice the length of the others. Second to the fifth articulations inclusive 

 short. Upper lip forming a triangle with the angles truncated, bordered with short 

 distant, stiff, cilia-like hairs. Mouth round. Eyes consisting of a black spot on 

 each side of the oral segment. Terminal or anal segment, simple, cylindric, 

 truncate. Intestinal canal simple, (no gizzard,) tortuous, capacious, most dilated at 

 the seventh articulation. Ciliary movement observable in the last two segments, 

 apparently within the termination of the intestine. Generative apparatus? 



Length five lines, greatest breadth one-third the length from the head .011 in. 

 Length of setae of fifth articulation .018 in. to .0255 in.; length of the others average 

 .012 in. 



Animal very active, found among algae in fresh water rivulets. 



2. Nais rivulosa. Fig. 2. — Body yellowish white, attenuated at the extre- 

 mities, most usually in the state of division. Anterior division with twenty 

 articulations, each furnished laterally with a fasciculus of five or six retractile podal 

 spines, which are elongated sigmoid and terminate with a double hook, length 

 averaging l-250th in. Articulations posterior to the fourth furnished on each side 

 with two moderately long setse, about l-75th in, in length; one of them frequently 



• Die Wiirraer der siissen und salzigen Wassers, 1771. Diet. Univ. d'Hist. Nat. t. 8, p. 566. 

 t Bui. tie PAcad. royale des Sciences et Belle-lettres de Bruxelles, 1838 t. v., p. 16. 



