and of nearly equal length; all the segments, except the two
terminal ones, thickly clothed with serrated spines. _Second cirrus_
considerably shorter than the third cirrus: anterior ramus with the
seven basal segments very protuberant, and paved with bristles, and the
four terminal ones on the usual structure; posterior ramus, with the
five basal segments paved (but much less thickly than in the anterior
ramus), and the nine terminal ones on the usual structure. _Third
cirrus_, the anterior ramus, with the five basal segments, thick and
paved, and eleven terminal segments on the usual structure: posterior
ramus, with one basal segment paved, and sixteen other segments on the
usual structure. In the posterior rami, however, of both the second and
third cirri, it is difficult to draw any distinct line between the paved
segments and the others.

_Caudal Appendages_, short, either just exceeding in length the pedicels
of the sixth cirrus, or equalling only the lower segment: segments
flattened, cylindrical, six in number, there being, in the same
individual, twenty-one segments in both rami of the sixth cirrus.

6. LITHOTRYA VALENTIANA. Pl. VIII, fig. 5.

CONCHOTRYA VALENTIANA. _J. E. Gray._ Annals of Philosoph., vol. x
(new series), 1825.

_L. scutis in profundam tergorum plicam invertis: tergorum opposito
superiore margine, plica altera aeque profunda instructo: carinae crista
prominente centrali, marginibus quadratis, in parte superiore: rostro
rudimentali: lateribus et pedunculo ignotis._

Scuta locked into a deep fold in the terga; the latter having a second
equally deep fold on the opposite upper margin. Carina with a prominent,
central, square-edged ridge in the upper part: rostrum rudimentary.
Latera and peduncle unknown.

Animal unknown.

Red Sea, imbedded in an oyster-shell. British Museum.

_General Remarks._--The two specimens in the British Museum are small,
and in an imperfect condition, without the peduncle or the latera, and
without the body of the animal. The capitulum so closely resembles that
of _L. truncata_, that it is quite superfluous to do more than point
out the few differences. It is just possible, though not probable, that
this form may prove to be merely a variety or younger state of _L.
truncata_, in which case this latter name would have to be sunk. The
difference, though one only of degree, in the form of the terga of the
two species is conspicuous, and there is a sl