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Show 1 9 0 5 . ] SPECIES OF WORM FROM THE RED SEA. 5 5 9 The prostomium, wTas frequently difficult to define accurately, owing, of course, to a protrusion of the buccal cavity. In three specimens, where its characters were very plain, I observed two conditions. In two individuals the prostomium was continued over the first segment of the body by grooves extending over about half that segment; in the other there was no such extension backwards of the prostomium. As both of these specimens were immature, I have 110 positive reason for asserting that they are not different species. But existing knowledge of this genus does not favour the supposition that two species live in common in one limited area. I should prefer, therefore, in the meantime to regard the character of the prostomium as variable in this particular. The prevalent arrangement in the genus is an epilobic or (as I prefer to call it) epicheilous prostomium. But one species, P. insularis, is reported to have no process of the prostomium, and also a variety of the type form P. matsushimensis * described by Dr. Micliaelsen. But in this case the variety does not occur in the same locality as the type. The setai, as is usual or universal (?; in the genus, are paired, and the two setae of the ventral pair clcse:1 together than those of the lateral pair. On the xviiith segment, which bears, as in other species, the male pores, the most ventral seta of each ventral couple is present, but I did not detect the more dorsal seta of the couple. The clitellum in this genus usually embraces segments xiii-xvii. In the present species it very distinctly extends over the xviiith and to the very end of that segment. This is the first external feature which has led me to distinguish the present species as new and undescribed. The genital papilla?, confirm by their arrangement this point of view. It is true that 1 have examined only one fully mature worm and that the papillae are known to vary f among mature specimens. I find, however, that in no species already known is there a close approximation to the conditions which obtain in the species of Pontondrilus which forms the subject of the present communication For in the present species the genital papillae are very distinctly paired structures, and not single and median. Moreover, they lie in front of the male pores, and there are no papillae following the male pores which are so prevalent in the genus Pontodrilus. The paired papillae lie between segments xiii/xiv and xiv/xv. They correspond in position to the ventral setae. The anterior pair are decidedly larger than the posterior pair. These papillae are very flat and hardly, if at all, project beyond the adjacent surface of the body. The appearance when seen through a hand lens is shown in the figure (text-fig. 78, p. 560). The centre of each papilla is opaque, white, and either somewhat kidney-shaped (anterior papillae) or more rounded (posterior papillae). This is surrounded * Micliaelsen, Zool. Jahrb. Syst. Abth. xii. p. 220. ; ■f E .g . P. laccadivensis, sec Beddard in ‘ Fauna ot Maldive and Laccadive Arch, vol. i. pt. 4. |