few layers of growth are ever preserved. In _L.
truncata_, where the latera are represented by mere stiles, (like
strings of beads), and are even less in width than the rostrum, they are
imperfectly calcified.

_Microscopical Structure of the Valves._--The shelly layers are white,
and generally separate easily, so that in _L. dorsalis_ it is rare to
find a specimen with the upper part of the valves perfect. The valves
are so translucent, that in the thin margins, even the tubuli could be
sometimes distinguished. The valves are coated by strong yellow
membrane, which, after the shelly matter in _L. dorsalis_ had been
dissolved in acid, separated into broad slips, answering to each zone of
growth. On the lower margin of each slip, there is a row of closely
approximate spines, generally slightly hooked, pointed, 1/650th of an
inch in length, and 1/10000th of an inch in diameter; they arise out of
a little fold; all are furnished with tubuli of the same diameter with
themselves, running through the whole thickness of the shelly layers,
and attached, apparently, by their apices, to the underlying corium. As
the spines are very numerous, so are the parallel rows of tubuli. After
the shelly layers had been dissolved, there was left in _L. dorsalis_
(well seen in the latera), an extraordinary, conferva-like mass of
branching, jointed, excessively thin tubes, sometimes slightly enlarged
at the articulations, and appearing to contain brown granular matter:
other portions of the valves, instead of this appearance, exhibited
membranes or films with similar, branching, articulated tubes or vessels
attached to them: I have not seen this appearance in any other
cirripede. The yellow exterior enveloping membrane, with its spines, is
present in all the species of the genus; in _L. Rhodiopus_ these spines
are much larger than in _L. dorsalis_, and on the inner sides of the
carina they are trifid and quadrifid, and large enough to be conspicuous
with a lens of weak power.

_Peduncle._--The most remarkable fact concerning this part, is that the
outer tunic, together with the calcareous scales with which it is
covered, is moulted at each successive period of exuviation and growth.
I demonstrated this fact in _L. dorsalis_ and _L. truncata_, by removing
the old tunic and finding a new membrane with perfect calcified scales
beneath; and as these two species, (I obtained, also, pretty good
evidence in _L. Nicobarica_,) are at the opposite ext