being
more spread out.

_Caudal Appendages_ about half the length of the lower segments of the
pedicels of the sixth cirrus; truncated and rounded at their ends;
thickly clothed with long excessively fine bristles, so as to resemble
camel-hair pencils.

The _Stomach_, I believe, is destitute of caeca; in it was a small
crustacean.

_General Remarks._--I was at first unwilling to sacrifice Mr. Hind's
genus, Trilasmis, which is so neatly characterised by its three valves;
moreover, the present species does differ, in some slight respects, from
the other species of Paecilasma; but under the head of _P. fissa_ I have
shown how that species, _P. crassa_ and _P. eburnea_ are tied together.
The absence of terga, which are rudimentary in _P. crassa_, (and we
shall hereafter see, in _Conchoderma_, how worthless a character their
entire absence is,) and the arrangement of the spines in the upper
segments of the posterior cirri, are the only characters which could be
used for a generic separation.

_Genus_--DICHELASPIS. Plate II.

OCTOLASMIS.[32] _J. E. Gray._ Annals of Philosophy, vol. x, new
series, p. 100, August 1825.

HEPTALASMIS. _Agassiz._ Nomenclator Zoologicus.

_Valvae 5, quae fere pro septem haberi possent, scuto in segmenta plane
duo, ad angulum autem rostralem conjuncta, diviso: carina plerumque
sursum inter terga extensa, deorsum aut disco infosso aut furca aut
calyce terminata._

[32] From [Greek: dichelos], bifid, and [Greek: aspis], a shield,
or scutum. The name Octolasmis was given by Mr. Gray under the
belief that there were eight valves. Leach (as stated in the
'Annals of Philosophy,') had proposed, in MS., the name
Heptalasmis, and this is now used in the British Museum by Mr.
Gray, and thus appears in Agassiz's 'Nomenclator Zoologicus.'
Although, strictly, there are only five valves, I continued to
use, in my MS., the term Heptalasmis, until I examined the _D.
orthogonia_, where it was so apparent to the naked eye that there
were only five valves, the scuta in this species being less
deeply bifid, that I was compelled to give up a name so
manifestly conveying a wrong impression, and hence adopted the
one here used.

Valves 5, generally appearing like 7, from each scutum being divided
into two distinct segments, united at the rostral angle; carina
generally extending up between the terga terminating downwards in an
imbedded disc, or fork, or c