1905. | SPECIES OF WORM FROM THE RED SEA. 559 
The prostomium 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, | 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 reason for asserting that they are 
not different species. But existing knowledge of “this genus does 
not favour the supposition that two species live i in common in one 
limited area. 1 should prefer, therefore, in the meantime to 
regard the character 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 pecstomn ay 
and also a v. aviety 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 sete, as is usual or universal (?, in the genus, are paired, and 
the two sete of the ventral pair clcse- together than those of the 
lateral pair. On the xvilith 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 x1l1—XVil. 
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 papille confirm by their arrangement this point of 
view. Itis true that I have examined Dally one fully mature worm 
and that the papille are known to vary fT among mature specimens. 
I find, however, that in no species already known is there a close 
appr oximation 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 papille are very distinctly paired 
structures, and not single and median. Moreover, they lie in front 
of the male pores, and there are no papille following the male 
pores which are so prevalent in the genus Pontodrilus. The paired 
pa pillee lie between segments xili/xiv and xiv/xv. They correspond 
in position to the ventral sete. The anterior pair are decidedly 
larger than the posterior pair. These papille are very flat and 
hardly, if at all, project beyond the adjacent surface of the 
hody. 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 
papille) or more rounded (posterior papillz). This is surrounded 
* Michaelsen, Zool. Jahrb. Syst. Abth. xii. p. 220. 
+ E.g. P. laccadivensis, see Beddard in ‘ Fauna of Maldive and Laccadive Arch.’ 
vol.1. pt. 4. 
