obs, on the upper part of the
growing surface of the carina. Moreover, considerable portions of the
inner surfaces of the scuta and terga, are roughened with minute sharp,
imbricated points, apparently for the firmer attachment of the corium.
The roughened knobs at the rostral angles of the scuta, no doubt are
homologous with the teeth in a similar position on one or both scuta in
Lepas, and in some fossil species of Pollicipes, as in _P. validus_. The
other projections and roughened surfaces are peculiar to Lithotrya. The
growth of all the valves is, as in Pollicipes, simply downwards.

The _Scuta_ are triangular, with their umbones or centres of growth at
the apex; the tergal margin, as seen from within, is either nearly
straight or much hollowed out, accordingly as the scuta simply overlap
the terga, or are received in a furrow. In some of the species there is
a distinct pit for the adductor muscle, and in others this cannot be
distinguished.

_Terga._--These present great differences in shape; but all appear to be
modifications, (as seen internally,) of a rhomboidal figure, which seems
to be the normal form of the terga in the Lepadidae. Of the lower part of
the valve, the whole exterior surface, with the exception of a narrow
ridge running from the apex down to the basal angle, is hidden by the
overlapping of the scuta, latera, and carina.

The _Carina_, in outline is triangular, with the basal margin in some
species extremely protuberant. In the first four species, the internal
surface is concave, in _L. truncata_ and _L. Valentiana_ it is convex,
with a central raised ridge, and consequently the upper
freely-projecting portion of the valve, has a prominent central crest or
ridge; in _L. Nicobarica_ and _L. Rhodiopus_ there is only a trace of
this ridge. The rostrum, as before stated, is always very small; it, as
well as the latera, are most developed in _L. Nicobarica_, and least in
_L. truncata_ and _L. Valentiana_; generally only a few zones of growth
are preserved, and from their being enlarged at their basal serrated
rims, the rostrum sometimes appears like a few beads of a necklace
strung together.

The _Latera_ are remarkable from being placed over the carinal half of
the terga, in an oblique position, parallel to the lower carinal margin
of the terga. A section, parallel to the growth layers, varies in the
different species from elliptic to broadly oval, and in _L. Nicobarica_
it is triangular. Only a