LEE BARKER WALTON 31 



while representatives of the famiUes LumbricuKdas and 

 Tubificid*e usually exceed 20 mm. in length, while the 

 Naidid^e on the contrary are rarely more and usually much 

 less than 15 mm. in length. 



The form and position of the setse are the chief char- 

 acters relied upon for the separation of the genera and 

 species. These may be long and hair-like (capiUiform) , 

 short and straight (needle-like), or S-shaped (sigmoid), 

 and may terminate simply or in two hooks (biuncinate) . 

 A slight enlargement (nodulus) is usually present on all 

 biuncinate set^e. The accompanying diagrams represent- 

 ing a typical Naid together with the different forms of 

 set^ will prove of assistance in making clear the characters 

 used in the synoptic table which has been slightly modified 

 from Michaelsen (:00) who in turn adopted a large pro- 

 portion of it from Vejdovsky ('84). The reproductive 

 organs have not been sufficiently studied to admit of a 

 final conclusion concerning their typical arrangement. 

 This includes all genera known up to the present time, 

 those occurring in North America being printed in heavier 

 type. Since the pubHcation of this monograph by 

 Michaelsen one new genus (H^emonais) has been founded 

 by Bretscher, while Michaelsen (:03) has proposed the 

 name Vejdovskyella for Bohemilla, the latter being pre- 

 occupied. 



FAMILY NAIDIDAE 



1791. Nats [ex Ord. Mollusca, e Class. Vermes] (part) Gmelin, Syst. Nat., 



vol. 6, p. 3120. 



189 J. Naiddmorpha (e Group Microdrili) Beddard, Monogr. Olig., p. 275. 



1900. Nahlidx Michaelsen, Monogr. Olig., Das Tierreich, Lief. 10, p. 16. 



190}. Naididie Michaelsen, Die geogr. Ycrbreit. d. Olig., p. 41. 



190 J. Naidid(s Michaelsen, "Zur Kenntnis d. Naididen," Zoologica, vol. 18, 

 p. 350. 



Set*e aggregated together in 2 or 4 bundles on a segment. 

 Dorsal bundles composed of capilliform, short needle-like, 

 or sigmoid (the latter biuncinate) SQtx; dorsal bundles 

 often absent; ventral bundles composed of sigmoid biun- 

 cinate set^e. Dissepiments well developed. Brain, com- 

 missure, and ventral nerve-cord well developed, distinct 

 from the hypodermis. Esophagus without muscular 

 stomach. Nephridia large, occasionally entirely absent. 



