188 Prof. M‘Intosh’s Notes from the 
have straight shafts and tapered winged tips bent at a slight 
angle. The bristles of the third tutt have in the peculiar 
group aslightly curved tip (sickle-shaped) with the serra- 
tions only at the tip, as described by Caullery and Mesnil 
in Spirorbis cancellatus. The bristles of the posterior region 
have broad tapering tips, bent nearly at a right angle, with 
the edge coarsely serrated. 
The branchiz are about four in number on each side, and 
do not offer any noteworthy peculiarity. 
The operculum is circular and hollowed out distally like 
a saucer, with a short stalk or process like a reversed cone. 
In young examples it is circular, forming a saucer-shaped 
dise, but in the older forms it is sometimes nail-shaped— 
that is, the circular shape is lost by an extension of one edge 
toward the stalk. Externally is the clear outer investment 
of the rim of the operculum, within which is a radially 
arranged layer at right angles to it; then follows a broad 
belt of circular fibres with strong longitudinal fibres con- 
verging to the stalk. The calcareous investment is very 
brittle. 
The tube is vitreous and peculiarly coiled, so that the 
aperture is on the summit of the spire. The whorls are 
boldly ridged, and the ridges affect the shape of the aperture, 
which is sometimes transversely elongated. The whorls 
form a conical mass with a flattened under surface, in 
the centre of which is the primary coil. The shape is thus 
like an irregular blunt cone, and the shell is very hard and 
glistens like pinkish porcelain. 
The Spirorbis violaceus of Levinsen somewhat resembles 
the bluish S. vitreus, O. Fabr., from the Arctic seas, as 
usually observed on pebbles and stones, the aperture in both 
tubes 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 type. Both differ essentially 
from the present species. 
It also diverges from the S. violaceus of Levinsen in having 
a more or less distinct gap above the crenulate web at the 
base of the tip of the collar-bristles, and in the same way 
differs from the older specimens mentioned and figured by 
Caullery and Mesnil. Nosimpleserrate tip was observed in 
any example, though some have a differentiated base with- 
outadistinct gap. The operculum does not differ materially 
from the figures and descriptions of S. violaceus given by 
the French authors just mentioned, the ringed condition 
and saucer-shaped tip being evident. 
