erm.) Valves four, horny: peduncle clothed with persistent,
horny spines.

Body partly lodged within the peduncle; mandibles with three teeth;
maxillae with two obscure notches; outer maxillae pointed; olfactory
orifices prominent; caudal appendages multiarticulate.

_Male and Complemented Male_, parasitic within the sack of the female or
hermaphrodite; mouth and thorax seated on a long tapering peduncle, but
not enclosed within a capitulum; mouth with normal trophi, but palpi
small and almost rudimental; cirri rudimental, reduced to two pairs;
penis reduced to a pore; caudal appendages rudimentary.

Attached to fixed littoral objects: Eastern Hemisphere.

_General Remarks._--As there are only two species as yet known, and as
these resemble each other in every respect most closely, a generic
description would be a useless repetition of the full details given
under _Ibla Cumingii_. I have taken this latter species as the type,
from having, owing to the kindness of Mr. Cuming, better and more
numerous specimens. Ibla and Lithotrya are the only two recent genera in
which the body of the animal is lodged within the peduncle; but there is
no distinction of any importance, though useful for classification,
between the capitulum and peduncle; and these two parts, as we have
seen, tend to blend together in some species of Conchoderma and Alepas.
The entire absence of calcareous matter in the valves and spines of the
peduncle, at first appears very remarkable; but we have seen a similar
fact in Alepas, and there is an approach to it in some varieties of
_Conchoderma aurita_ and _C. virgata_. In all four valves of Ibla, the
umbones, or centres of growth, are at their upper points. The horny
spines on the peduncle, are the analogues of the calcareous scales in
Scalpellum and Pollicipes; and in this latter genus, two of the species
have their scales, almost cylindrical, placed irregularly, with new ones
forming over all parts of the surface, and not exclusively at the
summit,--in which several respects there is an agreement with Ibla. The
shape of the body (_i. e._ thorax and prosoma, Pl. IV, fig. 8 _a'_) is
peculiar; but it is only a slight exaggeration of what we have seen in
several genera, and shall meet again in some species of Scalpellum. The
presence of hairs on the outer membrane of the prosoma is a peculiarity
confined to this genus amongst the Lepadidae, though observed in the
sessile genus, _Chthamalus_. The cauda