LEPAS CŒRULESCENS. _Spengler._ Skrivter af Selskabet, 1 Bind.,
1790.[111]
[111] The longitudinally folded walls, as described by Spengler,
the blue colour, the habitat, namely, associated with _B.
tintinnabulum_ from the East Indies, and more especially the
expression "Valvulæ operculi cardine dentato mobilis," apparently
referring to the highly prominent articular ridge of the scutum,
leave little doubt on my mind that I have rightly named the present
species.
_Shell with the upper part tinged greenish-blue, longitudinally ribbed:
radii moderately wide, with their summits oblique: scutum with a small
adductor and extremely prominent articular ridge, united together and
so forming a small sub-cylindrical cavity: tergum with the spur not
joined to the basi-scutal angle._
_Hab._--Philippine Archipelago, attached to _Balanus tintinnabulum_;
attached to a ship's bottom, and to _Balanus tintinnabulum_, both
from the Pacific Ocean; attached to a massive coral, and associated
with _T. vitiata_, and therefore from the tropical eastern seas; Mus.
Brit., Cuming, Stutchbury.
_General Appearance._--Shell conical, sometimes depressed; surface
with rather broad, smooth, longitudinal ridges; whitish, with the
upper part greenish-blue, sometimes very feebly tinted with pink;
radii white, or mottled with blueish-green, or with pink. When the
outer lamina of shell has been corroded, the upfilled parietal tubes,
of a dull blueish-gray colour, are exposed. The radii are moderately
wide, with their summits very oblique. In basal diameter, one
specimen was 1.8, and another 1.5 of an inch.
_Scuta_, externally furrowed very slightly in a longitudinal
direction, causing the lines of growth to become a little sinuous.
The valve is strong and thick; and the epidermis, when preserved,
is hirsute with spines. The articular ridge is extraordinarily
prominent; it projects, as measured from the external surface of
the valve, to an amount equalling half the width of the valve in
its widest part. The adductor ridge is very short, and is united
to the bottom of the articular ridge, thus forming a small, nearly
cylindrical tube, which runs up to near the apex of the valve. The
inflected occludent margin is broad and coarsely toothed. The crests
for both depressor muscles are not very prominent. When the scuta
and terga are articulated together, owing to the great projection of
the articular ridge of the scutum, its upper part is separated from
the tergum (fig. 4 _b_), by a remarkably wide and deep, fissure-like
hollow. The scutum, in some distorted specimens from a ship's bottom,
was narrow in proportion to its ordinary breadth.
_Terga._--These are large. Externally, there is a broad, longitudinal
depression, bounded on each side by a ridge. The carinal half is
feebly striated longitudinally. A large upper portion (fig. 4 _b_)
projects freely, and stands, when the two valves are articulated
together, above the apex of the scutum, but does not form a beak as
in _T. porosa_. Internally, the tergal margin is widely inflected;
the articular furrow is very deep, but the articular ridge is not
prominent. The spur is not very broad; it is separated from the
basi-scutal angle by a small space of basal margin, which forms a
straight line with the basal margin on the opposite side of the spur.
The end of the spur is truncated, and is parallel to the basal margin.
_Structure of the Shell and Radii._--The walls are thick: the
parietal tubes are rather large and regular; they become solidly
filled up in their upper parts. The sutural edges of the radii are
formed by unusually narrow, sinuous ridges, sending off delicate
denticuli on each side: the interspaces between these ridges are
solidly filled up. The crenated edges of the alæ are rather thick.
Neither the _mouth_ nor the _cirri_ offer any noticeable character;
but I may observe, that, in the mandibles, the third and fourth teeth
are close together; and that, in the three posterior cirri, the tufts
of small spines between the main pairs are small.
_Affinities._--This species is very distinct from the others, with
the exception of the following _T. radiata_, to which it is in
several respects allied. The under side of the scutum, with its great
articular ridge, and the cylindrical tube formed by the union of the
latter with the short adductor ridge, affords the most noticeable
character.