PIXELL—POLYCH ATA OF THE INDIAN OCEAN 795 
it is always, however, longer than the other branchiz. There is a small rudimentary 
operculum on the side opposite the functional one. 
The thorax has the usual seven segments, the collar fascicle being composed of about 
a dozen of the typical sete (fig. 1b) with an equal number of smaller ones with narrow 
blades. The collar itself is deep, the ventral lobe generally entire, though sometimes 
notched and variously folded or crumpled. The thoracic membrane is well developed ; in 
two or three of the specimens the posterior ventral free part is nearly as long as the 
whole thorax. 
The abdomen has about 80 segments ; its greatest width is 2 mm. 
The uncini have the usual shape and five or six teeth ; the abdominal setze (fig. 1c) 
are in groups of eight. 
This species has apparently rather close affinities with H. bispinosa, Bush (8) from 
Bermuda. ‘There are, however, no figures nor sizes given of this species and from the 
description there seem to be several points of difference (8, p. 496). 
4. Hydroides heteroceros, Grube (22) 1868 (Plate 8, fig. 2). 
Serpula (Hydroides) uncinata, Gravier (21) 1908 ; non Philippi (40) 1844. 
Eupomatus heteroceros, Willey (50) 1905. 
Specific characteristics: the opercular funnel has about 30 well-marked serrations 
and the central crown nearly always consists of seven long stiff spines; six have lateral 
hooks; the seventh is generally larger and curved over the others and has no lateral 
processes (figs. 2a and b). 
Localities. Several specimens from wall of Suez Quay; one from Suakin Harbour 
obtained by divers; and two from a depth of 10 fathoms off Zanzibar. 
Tubes thick, flattened on side of attachment, often coiled, marked by faint longi- 
tudinal lines, aperture circular. 
Length variable ; the largest specimens were about 40 mm. long and 4 mm. wide, but 
most are only three-fourths of this size. 
“The body is generally of a dull yellowish colour; the branchize have dark crimson 
bases but are light yellow distally. There is, however, a great deal of variation in colour, 
the gills occasionally appearing purple and orange. The pedicle of the operculum is 
banded with crimson and white alternately.” The functional operculum is not necessarily 
on the right as given by Gravier. In two specimens it appeared on the left and is no 
doubt subject to reversal after loss (Zeleny 51). 
The rudimentary operculum is short with a terminal knob showing six or seven radial 
constrictions. 
The serrations round the outer opercular funnel have laterally elongated terminal 
processes sometimes produced into sharp teeth at the sides. In two out of the seven 
specimens examined there were only five spines with the lateral hooks in addition to the 
large curved plain one, instead of the usual number six—there is also a great deal of 
variation in the position of these lateral hooks. In some, they are about half-way down 
(figs. 2a and b) as figured also by Gravier* (21, fig. 286) and described by Willey (50), 
* There can be no doubt, I think, that Gravier’s figure and descriptions of 1. wncinata refer to this 
Species; they differ considerably from the true Hupomatus wneinatus. 
10—2 
