390 SPIRORBIS VIOLACEUS. 
being at the circumference of the flattened disc, whereas in S. Caulleryi it is generally on the 
summit of the elevated spire in the centre of the shell. The two narrow ridges of S. Caulleryr 
also diverge from the broad, rounded elevations of S. violaceus. 
There is considerable difficulty in reconciling the various descriptions of S. violaceus, 
Levinsen (1883), with the form under consideration. He describes four thoracic segments, 
each with dorsal bristles. Those of the collar-segments have a broad or dilated wing to 
the tip, so that it is obliquely triangular, acuminate, and with serrations and striz. The 
base of the tip is rounded, not angular as in S. spirillum, with which it agrees in having no 
“bite.” The basal serrations are coarser than those above. The pectiniform uncini of the 
anterior region, usually distinctly toothed in other forms, have a margin minutely striated 
transversely, but without teeth. No mention is made of the operculum. The tube has three 
distinct coils, the exterior not coming from the base; one or two being visible, and never 
ascending. There are two deep grooves, and three rounded ridges, the ends of the latter 
affecting the aperture. Levinsen’s species somewhat approaches S. vitreus, O. Fabricius, 
from the Arctic seas, as usually observed on pebbles and stones, the apertures of the tubes 
of both species being on the summit of the coils, but the camerated condition of the sulci 
of the outer whorls in the Arctic form is not seen in the southern species. Miss Bush enters 
S. vitreus as a British species, viz., from Devonshire on shells, but there may be confusion 
between this and S. violaceus. Again, Levinsen states that the tube of S. witreus, with the 
exception of the keels and foramina, is similar to that of Spirorbis cancellatus, O. Fabricius, 
though in two examples he examined the dorsal bristles of the fourth segments were absent, 
and the striz of the bristles of the collar were less distinct. Sterzinger (1909) again figures 
the operculum as conical, whilst the collar-bristles, as shown by Caullery and Mesnil, have 
‘a gap, fine serrations occurring on the basal web, coarser serrations on the distal blade. The 
sickle-shaped forms are serrated along the concave (anterior) edge. The cancellated margin 
(as 1f punctured) of the dextral, vitreous, translucent, boldly ridged tube is noteworthy. 
In the presence of a distinct though modified gap or “ bite” above the crenulate web 
at the base of the tip of the collar-bristles it diverges from Levinsen’s type, though it agrees 
with the older specimens mentioned by Caullery and Mesnil. Some of these bristles show 
a differentiated base without a distinct gap, and thus there is considerable variety. The 
operculum does not materially differ from the figures and description of S. violaceus given by 
the French authors, the ringed and saucer-shaped tip being evident. 
The Serpula granulata of O. Fabricius in the structure, arrangement and colour of the 
tube appears, as Levinsen states, to come near this form. It was found under stones and 
on Balam and Mytilo. 
Fleming (1825) refers to a species mentioned by Montagu, and which he terms after its 
discoverer S. Montaguz, as having one very thick, rounded, glossy, white volution. The shell 
is very convex, and wrinkled transversely, with a minute central cavity at the top, sometimes 
only a suture. The animal is of a buff colour, with ten ciliated rays, and a sub-funnel-shaped 
operculum, having a brown, ciliated hyaline margin. It was procured on a Haliotis from 
Guernsey. 
In Brown’s ‘Illustrations of Conchology’ (1827) the figure of Spirorbis conicus (Plate I, 
fig. 58) resembles this species. 
Fauvel (1909) observes that the tubes of this form are common on large pebbles of sand- 
