imple.

_Cirri_, with twice as many segments in the sixth cirrus as in first;
spines on the first and second cirri doubly serrated.

_Colours_ (when alive).--Capitulum and peduncle grey, with a tinge of
blue, with six black bands, tinged with purplish brown. The two bands
near the carina become confluent on the peduncle, and sometimes
disappear; the carina is edged, and the interspace between the two
scuta, coloured with the same dark tint. The whole body and the pedicels
of the cirri are dark lead-colour, with the segments of the cirri almost
black: in some specimens, the colour seems laterally abraded from the
cirri. Ova white, becoming in spirits pinkish, and then yellow. The dark
bands on the capitulum and peduncle become in spirits purple; but are
sometimes discharged; the general grey tint disappears. Professor
Macgillivray states that many individuals are light-brown or
yellowish-grey, with irregular brown streaks, or crowded dots: he states
that in very young specimens the colours are paler, and the valves
spicular.

_Size._--The largest specimen which I have seen, had a capitulum rather
above one inch long and three fourths of an inch wide: growth very
rapid.

_Monstrous Variety._--In the British Museum, there is a dried and
somewhat injured specimen of a monstrous variety, the _Pamina
trilineata_ of J. E. Gray: it differs from the common form only in
having a tubular projection, just behind the notch separating the upper
points of the terga; this tube springs from over the terga, and is,
therefore, in a different position from the ear-like appendages in
_Conchoderma aurita_. It does not open into the sack: the membrane
composing it appears to have been double in the upper part, and to have
been lined with corium: in short, this tube seems to have been an
excrescence or tumour, of a cup or tubular form.

_General Remarks._--It will have been seen how much subject to variation
the valves of this species are. When I first examined the _Cineras
chelonophilus_ of Leach, from 36 deg. N. lat., Atlantic Ocean, and found
in many specimens, both old and young, that the terga were very small,
flat, acuminated at both ends, with a projecting shoulder on the carinal
margin, and situated at about their own length from the apex of the
carina, and at twice their own length from the scuta; and when I found
the carina acuminated at both ends, and the scuta very imperfectly
calcified, with the lateral lobe broad, flat, and