DESCRIPTIONS OF GENERA AND SPECIES 293 



(5) Pristina proboscidea, new species. 



Definition. Dorsal setae capillary. Prostomiwm very large as in N. lacustris. Hab. — 



S. America. 

 On a casual glance this would be undoubtedly referred to the species N. lacustris. 

 As BouENE has found in N. lacustris dorsal setae occasionally present on some of the 

 segments normally devoid of them, the present worm may be an extreme variation. 



Genus Ripistes, Dujaedin. 



Pterostylarides, Czeeniavsky. 

 Stylaria, O. Schmidt (in part.). 

 Nais, Geebnitzky (in part.). 



Definitioit. Prostomium elongated. Dorsal setae commence in the sixth segment, 

 the first three pairs of bundles containing setae of great length ; ventral setae 

 commence in the second segment, but are absent from IV and V. Eyes present. 



Though neither Vejdovskt (24), nor Vaillant (6) accept this genus, I think that 

 BouENE (5) is quite right in emphasizing its distinctness from Stylaria. But in using 

 Czeeniavskt's name Pterostylarides, the name Ripistes of Dujaedin, which clearly 

 has the priority, was overlooked (as Vaillant, 6, p. 366, has pointed out). 

 Czeeniavskt's definition does not include a reference to what is really the most 

 important character of the genus, viz. the absence of both dorsal and ventral setae 

 from segments iv and v. But the description of the three pairs of extremely long 

 dorsal setae leaves no room for doubt as to the identity of Pterostylarides and 

 Ripistes. The characters of the cerebral ganglia strengthen the arguments for 

 regarding ' Stylaria parasitica ' of 0. Schmidt as the type of a genus distinct from 

 Stylaria. It is, according to Vejdovsky's figure (24, PI. ii, fig. xo), very short — not 

 prolonged backwards, as is the case with Nais. There are two species, viz. R. para- 

 sitica and R. macrochaeta. 



(i) Ripistes parasitica (0. Schmidt). 



Ripistes sp., Dujardin, Proc.-Verb. Soc. Philom. Paris, 1842, p. 93. 

 Stylaria parasitica, 0. Schmidt, Froriep's Notizen, iii, 1847, p. 331. 

 Nais parasitica, Geebnitzky, Zapiski novoross. Obstch. Est., 1873, p. a68. 

 Pterostylarides parasitica, Czeeniavsky, Bull. Soc. Nat. Mosc, 1880, p. 310. 

 Definition. Length, 6 mm. ; number of segments, 20 ; prostomium about as long as peristomial 



