282 



OLIGOCHAETA 



papillae can occur in species which differ in other comparatively important ways, 

 they cannot be of such use for the purposes of generic definition as Vbjdovsky would 



have it. 



As to the identity of Ophidonais with Slavina, which Bousfield argues, and which 

 Stolc and Bouknb dispute, I think it must be upheld. The only difference between 

 the genera is in the setae; in Ophidonais the dorsal setae are all short and straight 

 with a cleft extremity. If the dorsal setae of Ophidonais were peculiar to the single 

 species assigned to that genus, this character would be unquestionably of some impor- 

 tance ; but, as a matter of fact, the two forms are the two extremes met with in the 

 genus Fais as defined here ; for Nais elinguis is exactly intermediate, having both 

 kinds of setae in the dorsal bundle. Finally, as to Stylaria: really the only dis- 

 tinguishing feature of this genus is the long prostomium; this structure has led to 

 its being confounded with Ripistes (q. v.), with which it has not much in common. 

 I do not believe that this character is sufficient to distinguish it as a genus distinct 

 from Ifais. There is also a Pristina with a long proboscis that does not otherwise 

 differ from its congeners — an argument from analogy. Minor has urged differences 

 in the way of asexual reproduction; but as Vaillant has pointed out, he did not 

 always find a distinction between the ' gemmiparity ' of Stylaria and the ' scissiparity ' 

 of Nais. 



As thus constituted the genus Nais will include the following well-characterized 

 species : — 



(i) Nais barbata, MiJLLEK. (6) Nais appendiculata, d'Udekem. 



(a) „ elinguis, Mullek. • (7) „ lurida, TiMM. 



(3) „ laeustris, Linn6. (8) „ josinae, Vejdovsky. 



v'(4) „ serpentina, Mollee. ^, (9) „ heteroehaeta, Benham. 



(5) » gracilis, Leidy. j (10) „ reckei, Floeeicke. 



In addition to these there are a number of worms which are very possibly members 

 of this genus, but of which no sufficient descriptions exist. These species may be first 

 considered. 



The Nais fusea of Carter (Ann. and Mag. Nat. Hist. (3), ii. p. 20), from its habitat might be 

 supposed to be distinct had it not been shown that these smaller OUgochaeta have often a wide 

 range. Its chief difference from Nais elinguis is, as Vaillant has indicated, the absence of eyes; 

 pending further information it may there be regarded as doubtfully distinct. 



A number of other species have been provisionally referred to this genus by Vaillant ; some 

 of these, however, are clearly not referable to the genus, while others are insufficiently characterized 

 to permit of their generic position to be stated with any approach to accuracy. They will be found 

 cited on other pages. 



