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Show 1892.] AQUATIC OLIGOCHiETOUS WORMS. 353 The worm consisted of eight segments, after which came a bud that had been in part detached ; but I succeeded in finding the rest of it upon the slide ; the number of segments, therefore, is approximately the same as Leydig gives for Molosoma niveum, and the same number also that Vejdovsky gives for Molosoma variegatum. The prostomium, however, was large, squarish in front, and distinctly wider than the rest of the body. Leydig figures a very inconspicuous prostomium-, which, in front at least, is actually narrower than the succeeding segments. With regard to the colourless oil-drops in the integument, I could see no structures that were at all obvious. There was no appearance such as is represented in Leydig's figures. Nor were there any clearly defined droplets such as Vejdovsky figures in his Molosoma variegatum. I should be inclined to say that there were no oil-drops present at all. The epidermis was much more like that of a Naid or a Chcetogaster than an Molosoma ; and even when the worm was treated with potash, which produces such recognizable effects' upon the oil-globules of other species, no alterations were observable, except that the worm was stained a faint yellowish. And yet there is no doubt whatever that I am right in referring the Annelid to the genus Molosoma. In all other particulars it agreed with that genus. The prostomium was ciliated on the under surface, and the lateral ciliated pits are present. The mouth appeared to be situated rather further back than it has been usually figured for this genus ; the constriction which marks off the prostomium posteriorly was situated some little way in front of the actual mouth-opening. The most important difference, however, from Leydig's description concerns the setae. In all the species of Molosoma at present known, with the exception of Vejdovsky's Molosoma tenebrarum and (if it be really distinct from this) Molosoma leidyi2, there are only capillary setae present in both dorsal and ventral bundles. In the two species above mentioned cleft sigmoid setae are also to be found3. In the specimen of Molosoma niveum described here I have also found these sigmoid set*, and it is principally the fact of the occurrence of these setae which leads me to doubt the identity of this worm with Leydig's Molosoma niveum. Had they been present Leydig would hardly have overlooked them. The existence of these sigmoid setae also, I may point out, precludes the possibility of this worm being the young of Molosoma quaternarium, and 1 do not think that it has anything to do with Molosoma tenebrarum. In the first seta-bearing segment there were not any sigmoid setae, but four capilliform setae in each of the dorsal, and three in 1 " Note upon the Green Cells in the Integument of Molosoma tenebrarum," P. Z. S. 1889, p. 51. "Notes upon certain Species of Molosoma,"Ann. Mag. Nat. Hist., Oct. 1889. 2 F. W . Cragin, " First Contribution to the Invertebrate Fauna of Kansas," Bull. Washb. Coll. Lab. 1887, no. 8, p. 31. 3 I am not quite certain that the species described by me as Molosoma tenebrarum (P. Z. S. 1889, p. 51) is really identical with Vejdovsky's species; I could not detect the cleft at the end of the setae, and the colour of the oil-drops appears to be rather different. |