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Show 1892.] AQUATIC OLIGOCH^TOUS WORMS. 351 size. Leidy's specimen measured 1 line (=2 mm.), Vejdovsky's 8 m m . M y own specimen being somewhat intermediate in size perhaps removes this difference. But a more important difference remains, which is not alluded to by Vaillantl. In Vejdovsky's figure8 of Pristina longiseta no sharp line of demarcation is indicated between the prostomium and the first segment of the body, and in the description of the species3 he remarks :-" Der Kopflappen verjiingt sich allmalig zu einem konischen fadenformigen Riissel." On the other hand, Leidy's figure indicates a sharp demarcation ; the " proboscis " 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 prostomium and first segment of the body. It appeared to m e 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 a m not assured that Leidy's and Vejdovsky'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 m e to destroy the generic distinctions between Pristina and Naidium. Previous to the appearance of that paper they could be distinguished as follows :- Pristina : 1. Dorsal setae of segment iii. long. 2. Prostomium elongate. 3. Shorter dorsal setae not bifid. Naidium : 1. These setae not longer than others. 2. Prostomium short with lateral processes. 3. These setae bifid. But in Bourne's Pristina equiseta the first character is that of Naidium, and in P. breviseta there are bifid setae in the dorsal bundles much like those of 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 prostomial tentacle is not so distinct as in other species. I do not think, therefore, that these two genera can be any longer distinguished. iii. On ^Eolosoma niveum. The only description of this species was published nearly thirty years ago by Leydig4; it has since been met with by Timm5 , who 1 ' Anneles' in ' Suites a Buffon,' vol. iii. p. 360. 2 Loc. cit. pi. ii. fig. 13. 3 Loc. cit. p. 31. 4 " TJeber die Annelidengattung Molosoma," Arch. f. Anat. 1865, p. 360. 5 " Beobacbtungen an Phreoryctes, &c," Arb. z. z. Inst. Wiirzb. 1883, p. 155. 25* |