e larger than the anterior
cirri, which latter spring from points a little lower down on the
thorax. In the posterior cirrus figured, the great basal articulation
or pedicel, almost equals in length, and much exceeds in thickness, the
four segments of the ramus; these segments are furnished on their upper
dorsal edges with little brushes of spines, but have not even a trace of
the normally larger and far more important anterior spines. In one
specimen, the anterior cirrus had a large pedicel, carrying three
segments, like those of the posterior pair; but in another specimen, one
of the three segments showed traces of being divided into two, thus
making four imperfect segments; whilst on the corresponding side of this
same individual there were only two ill-formed segments, with their few
spines differently arranged. Again, in a third specimen, the great basal
segment of the anterior cirrus on one side, bore, exteriorly to the
usual ramus, a single segment furnished with bristles, and evidently
representing a second ramus; thus showing that the great basal segment
certainly answers to a pedicel. I may here add, that on the integuments
of these cirri, I observed with a high power, the serrated scale-like
appearance common in other Cirripedes. Directly between the bases of the
sixth cirrus, there is a very minute papillus, which, under the highest
power, can be seen to consist of two closely approximate, flattened
points; these, I have no doubt, are the caudal appendages in an
extremely rudimentary condition, for I traced the vesiculae seminales to
this exact spot: close outside these rudimentary points, on a slight
swelling, is the anus. It will presently be seen that in the male of the
closely allied _Ibla quadrivalvis_, the nature of these caudal
appendages admits of no doubt, for in this species they consist of more
than one segment, are spinose, and close under them towards the mouth,
there is a perfectly distinct papillus, representing the usual
probosciformed penis.

_Alimentary Canal._--The oesophagus is very narrow, and of remarkable
length; from the orifice under the mandibles, it first runs back (in
this respect not well represented in Pl. V, fig. 1,) under the bullate
labrum, and then straight down the peduncle, where it terminates in the
usual bell-shaped expansion, entering one side of the small globular
stomach; the latter, at its lower end, is slightly constricted, and then
is rather abruptly upturned. The