Gatty Marine Laboratory, St. Andrews. 173 
the non-bristled region in front of the ovigerous segments 
and bulge laterally, the region being thus characterised by 
its pallor. 
The masses of tubes formed by this species are often of 
large size, showing that by rapid budding it can hold its own 
in the struggle for existence, probably quite as effectively 
as in the case of those with large ova—these being few. 
The notion that the character of the tubes as to closeness 
and divarication may indicate specific distinction is uncer- 
tain. Much will depend on freedom from injury in the 
living or dead condition and the site inhabited. 
Not all the examples from St. Andrews have opercula. 
Some have none, the tips of all the branchie (eight) 
showing only a process enlarged at the tip, the granular 
cells being arranged in a somewhat regular manner and 
often hexagonal in outline. 
The prominent dorsal edges of the collar of the next 
species, Hydroides norvegica, Gunner, are supported by the 
first bristle-bundles, a considerable gap, however, occurring 
in the mid-dorsal line. It then passes ventrally to expand 
into a large thin lamella sloping on each side to a median 
notch, so as to be more or less bilobed, and is either 
reflected backward or stretched forward on the base of the 
branchie. 
The branchiz form two well-marked fans on each side of 
fifteen to eighteen filaments, the dorsal filament in addition 
on each side being modified either into a complete or a rudi- 
mentary operculum, and it seems to be immaterial which 
side develops the complete organ, since it is sometimes the 
one and sometimes the other. The branchial filaments are 
of moderate length, and taper distally to end in a short 
subulate process, often concealed when coiled. No special 
chordoid or other axial structure is present, but the 
cuticle is very thick. The pinne are rather short, devoid of 
a special stiffening apparatus, and extend to the tip, par- 
tially overlapping the terminal process. They taper a little 
from base to apex. 
In life the branchiz are spotted with crimson, and have a 
pinkish hue from the colour of the pinne. 
The pedicle of the operculum has a transparent but tough 
investment of a cellular membrane (mainly hexagonal). 
Internally is a yellowish fibro-granular apparently muscular 
cylinder in the preparations. The distal funnel or disc of 
the operculum is brownish and horny, and when viewed from 
above has somewhat the aspect of a Chinese umbrella with 
