1903.] MARINE FAUNA OF ZANZIBAR. 171 
The prostomium is, in this family, usually more or less reduced. 
In Chetopterus itself it is completely merged with the oral 
funnel, and the same condition is described for some Phyllocheeto- 
pterids (e. g. P. claparedi McIntosh). In all the members of this 
genus it is normally scarcely distinguishable externally, both pairs 
of tentacles being carried by the peristomium. In certain specimens 
of P. elioti, however, as described below, it is quite prominent, 
and so was discoverable in all the four species I have examined. 
The first body-region is an almost solid mass of muscular and 
glandular tissue in all species, but posteriorly musculature is 
confined to the ventral surface, except at the level of the parapodia, 
where muscle-bands surround the body. Between these the body- 
wall is excessively thin dorsally and laterally, and always black 
from the colour of the gut-walls. 
Up to the present six species have been described, viz. :— 
P. socialis Claparéde. Mediterranean and Atlantic (1) (4). 
P. major Claparéde. Mediterranean (1). 
P. gracilis Langerhans. Canary Islands (2). 
P. claparedi McIntosh. Japan (3). 
P. aciculigerus Crossland. The Maldive Islands (6), 
P. gardineri Crossland. The Maldive Islands (6). 
To these I now add :— 
P. elioti. Zanzibar. 
P. pictus. British East Africa. 
Claparéde’s P. fallax was founded on such characters as the 
numbers of segments composing the three body-regions, the 
ringing of the tube, &c.; these have been shown by Roule (4) to 
be variable in members of this genus. 
The principal distinctions of systematic importance are :— 
(1) Presence or absence of eye-spots, and of the development 
of the prostomium. 
(2) The number of the strong setz in the notopodium of the 
fourth setigerous segment. 
(3) The proportionate sizes of the parts of the parapodia of 
the regions B and C. 
(4) Ringing and other such details of the tubes are variable, 
but (1) in some species they are straight and occur 
singly, and (2)in others they are of a U-shape and occur 
in numbers twisted together. 
These characters are distributed as follows :-— 
(1) Eye-spots present in P. socialis, P. major, P. elioti, P. 
gardineri, P. pictus; absent in P. claparedi, P. aciculigerus, 
P. gracilis. 
(2) A single strong seta in 4th notopodium in P. socialis', 
P. major, P. claparedi, P. pictus. More than one seta 
strengthened. PP. gracilis with three, P. gardineri three, 
P. elioti two, and P. acieuligerus eight. 
1 In P. socialis two sete may exceptionally occur, but the extra one is always 
smaller than the one it accompanies. 
