Gatty Marine Laboratory, St. Andrews. 187 
considerably smaller, but their structure is the same. All 
the hooks when in position have their teeth directed forward. 
The tube is vitreous throughout the greater part of its 
thickness, but the inner lining is opaque white, and its shape 
is that of a long and sharp-pointed elephant’s tusk. The 
anterior aperture is neatly rounded, but not dilated, whilst 
by the gradual thinning of the outer layer a character is 
given to it. The posterior end presents a minute aperture. 
It measures from 25 to 385 mm. in length, and its wider 
region in front is from 2 to 2°3 mm. 
Various structures affect the external surface of the tube, 
such as corals, other Serpulids (for example, Hydroides, 
Serpula vermicularis, and Spirorbis), Polyzoa, and Sponges. 
It is a favourite site for Lepraliz. A southern variety from 
Bona Bay is considerably smaller, the largest being 25 mm. 
long, is characterized by its brownish hue. In the Zetlandic 
examples comparatively few abnormalities occur amongst 
hundreds. Occasionally a constriction of the shell is 
observed toward the wide anterior region, or the rings of 
growth here and there are unusually prominent. Under 
favourable conditions the delicate posterior end with its 
greater curvature is entire, forming a needle-like commence- 
ment to the tube. Rarely, as in certain Zetlandic examples, 
a lateral ridge on each side runs from the anterior aperture 
to the posterior end. 
A rather rare species is Spirorbis caulleryi, sp. n., from the 
under surface of stones in tidal pools in Guernsey and Herm, 
and in this the cephalic collar is normal and forms a sheath 
for the branchiz, which are seven or eight on each side. 
The body is typical in outline, and has seven bristled seg- 
ments. The first or collar-series consists of bristles which 
have no distinct gap at the base of the tapered terminal blade 
or a modified one. The former kind occurs in one group, 
the straight shaft shghtly dilates at the shoulder, from which 
the tip is bent backward and coarsely serrated, the serrations 
next the shoulder being perhaps less distinct than those 
which follow. The other group presents a distinct differentia- 
tion of the base of the terminal blade, the separated part at 
the shoulder having finer serrations, the edge beyond (bear- 
ing the distinct serrations) being separated by a distinct 
step. The base of the blade has five or six teeth at least in 
lateral view, and in antero-posterior view this part appears 
to form a spiked collar to the anterior edge-of the bristle. 
The serrations on the terminal blade vary, some having fine, 
others coarse points. The second bristle-tufts of the region 
