72 PERCY SLADEN TRUST EXPEDITION 
some other points there is agreement with the two specimens described by Gravier (21) 
from the Gulf of Aden. 
Only the one specimen from Diamant Island has as many as 50 serrations round the 
margin of the opercular funnel, and this is the number given by Saint-Joseph (44) as the 
minimum. The general number in these specimens is 30—40. 
Genera Hyprormpes and EuPpomMATUus. 
As so much confusion exists with regard to these genera, it has been necessary to 
endeavour to draw up some scheme of classification. The definitions givén by the 
authors who established them are so indefinite that it is almost impossible to decide into 
which, if either, to put many of the recently described species with the characteristic 
two-tiered opercula. 
The operculum, in each case, consists of an outer more or. less funnel-shaped part as 
in the genus Serpula with a varying number of radii ending generally in pointed teeth. 
From the centre, or near the centre, of this arises a crown of spines—these may be all 
alike (homoceros) or, as very frequently happens, one may be different from the rest 
(heteroceros). Further, these spines very frequently have secondary processes. The 
latter may occur internally and, in this case, especially if they are near the base of the 
spine, be difficult to see from the outside, or they may be lateral and therefore quite 
noticeable. Moérch points out that such characteristics of the spines are of sub-generic 
value (87, p. 372), but his definitions are not sufficiently definite to distinguish some of 
the more recently described specimens. Forms having lateral processes to their opercular 
spines have been already referred to the genus Hydroides by Bush (7) and some other 
authors. It seems best therefore to keep to this distinction and the genus Hydrordes will 
then include H. norwegica, for which Gunnerus (25) established the genus (describing the 
spines as “ bacillis teretiusculis, multispinosus”), and also many others. It would include 
quite well the genus Hucarphus, established by Morch, which appears only to differ in 
having the lateral processes terminal in position thus giving the condition “ bacillis 
planis...apice arcuato..., utrinque cornuto,” described by Mérch (87, p. 372). In another 
place (87, p. 378) Mérch draws attention to the fact that these lateral processes of the 
spines may be sub-terminal (“extremitate utrinque aurita, interdum aculeo intermedio 
terminali, unde uti cruciati”), and in such a position they are sometimes found in 
H. heteroceros both in the specimens I examined from Zanzibar and the Red Sea and 
in Grube’s specimens (22), though the more normal position is about half-way down. 
Thus either the species H. heteroceros and many others should be put in the genus 
Eucarphus, or else Eucarphus should be included in the genus Hydroides in which 
the secondary processes (hooks) on the spines may be terminal or not. The latter 
course, being more consistent with the laws of priority, is the one taken here. 
The genus Glossopsis also seems to be quite unnecessary. 7. mina, for which it was 
established by Bush (7), falls quite naturally into place in the Table given below, being in 
fact closely related to Hl. monoceros, Grav. 
The genus Hupomatus, Phil. “bacillis simplicibus apice leviter arcuato, sorta,” then 
