LEPAS CARIOSA. _Pallas._ Nova Acta Acad. Scient. Petrop. tom. ii
(1788), p. 240, Tab. 6, fig. 24.
_Parietes thick, formed by several rows of unequal-sized pores. Tergum
narrow, with the apex beaked, and spur sharply pointed._
_Hab._--Columbia River, west coast of North America, Mus. Brit.
and Cuming; Behring Straits (Capt. Kellett); the Kurile Islands,
according to Pallas. Attached to shells, and to each other in groups.
_General Appearance._--Shell steeply conical, with a rather small
oval orifice; or cylindrical, with a large rhomboidal and little
toothed orifice. Colour dirty white. Surface either simply rugged,
or more commonly covered by numerous, narrow, extremely prominent,
longitudinal plaits; from the manner in which these overlap each
other, the shell almost appears as if thatched with straw. The
upper corroded part of the shell usually exhibits a cancellated
and finely punctured surface. The radii are generally very narrow,
forming towards the base of the shell a mere narrow ribbon to each
compartment, and often hardly distinguishable; but in one specimen
they were of considerable width: in the former case, the alæ are
often widely exposed. The largest specimen which I have seen was 1.5
of an inch in basal diameter, but Pallas gives 2.2 as the measurement
of a specimen from the Kurile Islands.
The opercular valves are united to each other and to the shell by
unusually strong membrane; and the upper parts of both valves, in all
the specimens seen by me, have been much disintegrated. The _Scutum_,
in old specimens, is faintly striated longitudinally, but in some
there is hardly a trace of this: the occludent margin is furnished
with a few large knobs, not corresponding with every alternate line
of growth (as is usual with other species), but with every fourth or
fifth line. Internally, the articular ridge is moderately prominent
(in young specimens more prominent) and reflexed. The adductor
ridge is sharp and prominent; in the upper part it is confluent
with the articular ridge, but in young specimens can be seen to be
distinct; in the lower part it borders a large deep cavity for the
lateral depressor muscle, in the middle of which there is a very
slight longitudinal ridge; this cavity sometimes is almost closed or
arched over in its upper part. In one specimen, the basal margin of
the scutum was deeply hollowed out in the middle. The _Tergum_ is
remarkably narrow, with its apex produced into a triangular beak,
hollow within, and sometimes faintly tinged purple. A deep, closed,
longitudinal furrow runs down the valve. The spur is long, remarkably
narrow, and pointed. Internally, the spur is produced up the valve
as a ridge: the inflected scutal margin, and the prominent articular
ridge, are both nearly straight, and parallel to the spur. The crests
for the depressores are sharp and very prominent.
The _Parietes_ are very thick and strong: unlike every other
species of the genus, they consist of several very irregular rows,
of unequally sized, round or angular tubes (3 _b_). These tubes or
pores are generally short, and are at frequent intervals crossed by
transverse septa; they often rather deserve to be called cells than
tubes. New tubes are formed along the inner as well as along the
outer lamina. They are lined by dusky purple corium. The internal
surface of the parietes is smooth in the upper part, and in the
lower, it is reticulated by slight, irregularly branching ridges.
The carinal internal margin of each compartment projects a little,
as in the case of _B. crenatus_ and _balanoides_. The lower edge of
the sheath is either hollow beneath, or is united to the walls. The
_radii_ in one specimen were broad, with slightly oblique, jagged
summits; generally they are extremely narrow, forming more ribbons
along the lower edges of the compartments, barely extending up as
high as the sheath. They can sometimes hardly, or not at all, be
seen, until the shell is disarticulated: in rather young specimens
the sutural edge is sometimes quite smooth; in old specimens the
lower part of the edge has coarse arborescent septa, with the
interspaces filled up solidly, whilst the upper part is smooth.
The _alæ_ are conspicuous from the outside, owing to the little
development of the radii; but owing to the diametric growth not
having been great, the part added during such growth is narrow;
the summits of the alæ are only slightly oblique: the sutural edge
is coarsely crenated, with the teeth denticulated or slightly
arborescent.
_Basis_ membranous.
_Mouth_: labrum with only four very minute teeth: mandibles with four
teeth; the third tooth broader than the first; the fourth small.
Maxillæ, with the two upper spines placed on a slight prominence,
beneath which there is a small notch. _Cirri_ of a very dark colour
(much injured): the segments of the first, second, and third pairs
very broad and short, protuberant in front, and most thickly clothed
with spines; the third pair is very little longer than the second
pair: the sixth pair (in a large specimen above one inch in basal
diameter) had the segments broader than long, each furnished with
seven pairs of spines.
_Affinities._--This species, though very distinct, evidently comes
near to _B. balanoides_, especially to _var._ (_a_). By merely
doubling or trebling the irregular rows of short tubes in the
walls of _B. balanoides_, with their reticulated inner lamina and
longitudinally folded outer lamina, we should have the structure
exhibited in _B. cariosus_. We have seen, also, that in _var._
(_a_) of _B. balanoides_, the spur of the tergum is remarkably
sharp, as in _B. cariosus_. This species, also, in a very marked
manner approaches in many characters, especially in the opercular
valves, in the cirri, and to a certain extent in the shell and
basis, to _B. flosculus_, and even in external appearance to _var.
sordidus_ of the latter--an inhabitant of the opposite extremity
of the continent, namely, of Tierra del Fuego. Again, the tergum
to a certain extent, and the scutum in a singular manner, resemble
these valves in _B. nubilus_, showing an unequivocal affinity to
that species. With respect to the most remarkable character of the
species, namely, the several irregular rows of tubes or pores in the
walls, it deserves notice that in _B. crenatus_, which is certainly
closely allied to _B. balanoides_, the longitudinal septa sometimes
divide near the outer lamina, thus giving rise to a few additional
tubes. Of the above several species, to which our present species is
allied, _B. flosculus_ stands in the next section, and _B. nubilus_
and _crenatus_ in the last: hence we see that _B. cariosus_ has
singularly divergent affinities. The peculiar structure of the
parietes, together with the general appearance of the shell, made me
at the first moment suppose I was examining a Tetraclita (or Conia of
Leach); hence, also, it has arisen, that _Lepas cariosa_ of Pallas
has often been quite erroneously given as a synonym of _Tetraclita
porosa_.