1905.] SPECIES OF WORM FROM THE RED SEA. 559 



The prosiomium was 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 no positive I'eason 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. 1 should prefer, therefore, in the meantime to 

 regard the chai-acter of the prostomium as variable in this parti- 

 cular. 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. Michaelsen. But in this case the variety does not occur 

 in the same locality as the type. 



The setce, as is usual or universal (?; in the genus, are paired, and 

 the two setse of the ventral pair clc se / 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 ditellum 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 ixi'pillce confirm by their arrangement this point of 

 view. It is true that I have examined only one fully mature worm 

 and that the papilke are known to vary t 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 papilla? are very distinctly paired 

 structures, and not single and median. Moreover, they lie in front 

 of the male pores, and there are no j)aj)illas following the male 

 pores which are so prevalent in the genus Pontodrilus. The paired 

 papillse 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 



* Michaelsen, Zool. Jalirb. Syst. Abth. xii. p. 220. 



f E.g. P. laccadiveiisis, see Beddard in 'Fauna ot'Maldivc and Laccadive Arch.' 

 vol. i. pt. 4. 



