oblique crest) running
from the summit of the triangular growing surface to the tip of the
valve: in perfect specimens, the growing and the free horn-like portions
(the latter represented much too long in fig. 8 _a'_ and _b'_) are about
equal in length: the basal portion of one side of the scutum overlaps
the tergum.

_Terga._--The internal glowing surface (fig. 8 _b'_) is almost
diamond-shaped, and less in area than the sputa: external surface
rounded; internal surface of the free horn-like portion, slightly
concave.

_Colour and Structure of Valves._--The external surfaces of the scuta
and terga are yellow along the middle, plainly marked by zones of
growth, and finely ribbed longitudinally: the internal surfaces and
sides of the horns of the two valves, are coloured fine blue or purple;
in the terga, however, the internal surface is mottled with yellow. In
some specimens, especially in one from Tavoy, each zone of growth was
only very narrowly edged with blue. When a thin layer is removed from
one of the valves, the dark blue or rather purple appears by transmitted
light a beautiful pale blue; and it is a very singular fact, that this
blue portion is permanently turned by very gentle into a fiery red; the
same singular effect is produced by muriatic and acetic acids. This blue
part is much harder than the yellow; the latter exhibits, under a high
power, a folded structure, and is penetrated by a few tubuli, whereas
the harder blue portion has a cellular or scaled appearance. The spines
of the peduncle exhibit, in a smaller degree, similar phenomena.

_Peduncle._--This, as already remarked, cannot be distinctly separated
from the capitulum; it is much compressed; it is composed of unusually
thin and delicate membrane, transversely wrinkled and thickly clothed
with long cylindrical horns or spines of chitine. These horns (fig. 8
_c'_) are not the analogues of the spines which are articulated on the
external membranes of many Pedunculated and Sessile Cirripedes, but of
the calcified scales on the peduncle of Scalpellum and Pollicipes; for
they pass through the membrane (the underlying corium being marked by
their bases) and are persistent, being added to, like the valves, during
each successive period of growth. Their bases are concave, so that a
section of the layers of growth exhibits a series of pointed cones, one
within another. Each spine is nearly cylindrical, irregularly curled,
and nodose or slightly enlarge