The
calcified scales in the uppermost whorl (Pl. VIII, fig. 1 _b'_) are only
slightly larger than those in the second whorl; the scales in the
succeeding three or four whorls, are considerably larger than those
below, which latter very gradually decrease in size, till, low down on
the peduncle, they are barely visible to the naked eye. In this lower
part, they may be called calcareous beads; they stand some way apart
from each other; they are nearly hemispherical, smooth, translucent, and
furnished with a conical fang; some of the smallest were 1/325th and
1/400th of an inch in diameter. The upper scales vary somewhat in the
outline, the most usual shape being sub-triangular, with the lower
margin arched and protuberant; and this margin, in the two or three
upper whorls, is crenated with teeth, which are conical and sharp, after
exuviation, but soon become reduced to mere notches. The scales in the
uppermost whorl are usually nearly quadrilateral; the imbedded portion,
or fang of each scale, is, in all, produced into a blunt rounded point.
The basal calcareous cup (fig. 1 _a'_ and 1 _c'_) is well developed, and
is sometimes even half an inch in diameter. Before the cup is formed,
there is a row of small, flat discs (fig. 1, and like those in fig. 2
_a'_) attached to the sides of the burrow: but a full account of these
parts of the peduncle, and of the burrowing habits of this species, has
been given under the generic description.

_Size and Colour._--Full average-sized specimens have a capitulum half
an inch in width and height; the entire length, with the contracted
peduncle, being about an inch and a half. Valves coloured dirty white,
with the enveloping membrane, when preserved, yellow. The outer maxillae,
palpi, pedicels of the cirri, anterior faces of the segments, dorsal
tufts, caudal appendages, and penis, dark purple. Thoracic segments
brown. There is a purple spot between the bases of the first pair of
cirri.

_Mouth._--Labrum considerably bullate, equalling about half the
longitudinal diameter of the mouth; inferior part produced so as to
separate the mouth some way from the adductor muscle; crest with a row
of blunt teeth and hairs; central part depressed and flattened.

_Palpi_, rather large, separated from each other by only half their own
length; bluntly pointed, thickly clothed with spines.

_Mandibles_ (Pl. X, fig. 2), with twice as many pectinations, namely 15,
between the first and second main teet