1892.] AQUATIC OUGOCH^TOUS WORMS. 351 



size. Leidy's specimen measured 1 line (=2 mm.), Vejdovsky's 

 8 mm. My own specimen being somewhat intermediate in size 

 perhaps remov6s this difference. But a more important difference 

 remains, which is not alluded to by Vaillant \ In Vejdovsky's figure ^ 

 of Pristina longiseta no sharp line of demarcation is indicated be- 

 tween the prostoinium and the first segment of the body, and in the 

 description of the species" he remarks : — " Der Kopflappen verjUngt 

 sich allmahg zu einem konischen fadentonnigen Riissel." On the 

 other band, Leidy's figure indicates a sharp demarcation ; the " pro- 

 boscis " commences quite abruptly. So too, though perhaps to a less 

 extent, does d'Udekem's figure. The specimen examined by myself 

 resembles Leidy's figure much more than that of Vejdovsky. The 

 location of the " stomach " by Leidy in the viith segment may be 

 perhaps an error. I found, as Leidy has figured, tactile hairs to be 

 very abundant upon the anal segment as well as upon the prosto- 

 mium and first segment of the body. It appeared to me that the 

 prostomium was deeply grooved upon the under surface, the groove 

 becoming continuous behind with the mouth. In view of the slight 

 difference recorded above, I am not assured that Leidy's and Vej- 

 dovsky's worms belong to the same species ; the specimen seen by 

 myself evidently is identical with the worms described by Leidy and 

 d'Udekem. Prof. Bourne's paper, to which I have referred, seems 

 to me to destroy the generic distinctions between Pristina and 

 Naidium. Previous to the appearance of that paper they could be 

 distinguished as follows : — 



Pristina : 



\ . Dorsal setse of segment iii. long. 



2. Prostomium elongate. 



3. Shorter dorsal setse not bifid. 

 Naidium : 



1. These setse not longer than others. 



2. Prostomium short with lateral processes. 



3. These setse bifid. 



But in Bourne's Pristina equiseta the first character is that of 

 Naidium, and in P. breviseta there are bifid setse in the dorsal 

 bundles much like those oi Naidium. The only differential character 

 which remains is therefore the prostomial tentacle ; but in Naidium 

 luteum the prostomium is said by Vejdovsky to be " lang ausge- 

 zogen," and in P. longiseta, as figured by the same author, the pro- 

 stomial tentacle is not so distinct as in other species. I do not 

 think, therefore, that these two genera can be any longer distin- 

 guished. 



iii. On iEolosoma niveum. 



The only description of this species was published nearly thirty 

 years ago by Leydig*; it has since been met with by Tiram*, who 



^ ' Anneles ' in ' Suites a Buffon,' voL iii. p. 360. 



2 Loc. cit. ^1. ii. fig. 13. ^ Loc. cit. p. 31. 



* " Ueber die Annelideugattuiig Molosoma" Arcb. f. Anat. 1865, p. 360. 



^ " Beobacbtungeu an Phreoryctes, &c.," Arb. z. z. Inst. Wiirzb. 1883, p. 155. 



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