_Shell ribbed longitudinally, dirty white; radii extremely narrow,
smooth-edged; scutum having an adductor ridge._
_Hab._--New South Wales (Sydney and Twofold Bay); Van Diemen's Land;
tidal rocks, often attached to other Cirripedes, and associated
with _Balanus nigrescens_, _Tetraclita purpurascens_, _Catophragmus
polymerus_; Mus. Brit., Cuming, Stutchbury, and Darwin.
This species, of which I have seen specimens from the above three
localities, all exactly agreeing with each other, is perhaps the
Australian representative of _E. plicatus_, which seems to be confined
to New Zealand.[113] In all essential points it comes so near that
species, that I shall make the greater part of my description
comparative.
[113] I am bound to state that I have seen two specimens of _E.
plicatus_ marked Sydney, and one marked Moreton Bay, but in both
cases the collectors had visited New Zealand, so that a wrong
habitat by mistake might easily have got attached to the specimens
in question.
_General Appearance._--In external appearance there is considerable
difference from _E. plicatus_, for _E. simplex_ is generally of a
regular conical shape, of a dirty-white colour, with the surface well
preserved, having moderately wide, not very prominent longitudinal
ribs. The orifice is rather small and pentagonal. The radii are
extremely narrow or linear, with quite smooth edges; the sutures,
however, are always very distinct, and in the upper part, the alæ
are generally rather widely exposed, as viewed from the outside.
The largest specimen which I have seen was .7 of an inch in basal
diameter.
The _opercular valves_ are closely similar to those of _E. plicatus_,
but the _scutum_ is generally a little more elongated, and the
articular furrow not so deep: in accordance with this last fact,
the articular ridge in the _tergum_ is not so prominent as in _E.
plicatus_; but we have seen that these several characters are highly
variable in _E. plicatus_. The slope of the basal margin of the
tergum towards the spur varies in the present species, in a strictly
analogous manner, as it does in _Tetraclita porosa_.
_Structure of the Parietes and Radii._--The parietes are not so thick
as in _E. plicatus_; internally they are tinted pale purple; when
broken transversely, a row of microscopically minute orange-coloured
dots can generally be distinguished between the outer and inner
laminæ; and these evidently represent the orange-coloured layer in
_E. plicatus_. The sheath also exhibits a faint tinge of orange. The
radii are very narrow, and are quite smooth-edged, differently from
in _E. plicatus_. The edges of the alæ barely exhibit a trace of
being crenated.
In the body I could perceive no difference from _E. plicatus_,
excepting that in the third pair of cirri the two rami are like each
other, and do not support any coarsely pectinated, only serrated,
spines; but after what we have seen on the variability of these very
same characters in _Tetraclita porosa_, I dare not trust to them. The
three posterior pairs of cirri, also, seem here to be more elongated
in proportion to the others, than in _E. plicatus_.
_Affinities._--It is certain that this species is most closely allied
to _E. plicatus_; but as I have seen many specimens of the latter
brought by different persons from New Zealand, and as I have observed
in them no approach to the characters of _E. simplex_, which, in
specimens from three localities, also appear to be constant, I have
considered the two forms as specifically distinct. The present
species differs from _E. plicatus_, in its white, conical, moderately
ribbed, well preserved, smaller shell; and more especially in the
orange-coloured intermediate lamina of _E. plicatus_ being here
represented only by microscopically minute dots. But the radii being
smooth-edged, is the most important differential character, though in
_E. plicatus_, during its earliest growth, whilst still immature and
colourless, the radii are likewise smooth-edged.