_Shell folded longitudinally, greenish or white: radii of moderate
breadth, smooth edged: scutum without an adductor ridge: tergum narrow,
with the spur confluent with the basi-scutal angle._
_Hab._--New South Wales; Van Diemen's Land; New Zealand; very
commonly attached to littoral shells and rocks; associated with
_Balanus trigonus_ and _vestitus_; Mus. Brit., Cuming, Stutchbury,
Darwin.
_General Appearance._--Shell conical, generally rather steep,
occasionally depressed: walls longitudinally folded, sometimes very
deeply, sometimes only to a slight degree: colour dull greenish or
white. Radii of moderate width, with their summits very oblique,
smooth and slightly arched: alæ much exposed, with their summits
less oblique than those of the radii: the portion added to the alæ
during the diametric growth differs much in appearance from the other
portion. The scuta have the growth ridges but little prominent;
they are crossed by a faint longitudinal band of gray. The largest
specimen out of the many which I have seen, was under .4 of an inch
in basal diameter.
_Scuta_, destitute of an adductor ridge and of crests for the
depressor muscles: the articular ridge is moderate; but the
articular furrow is rather wide: the internal occludent margin is
much thickened. The _Terga_ are narrow and small; they are somewhat
variable in shape, caused by the degree to which the basal margin is
hollowed out (fig. 1 _c_-1 _e_), and likewise by the extent to which
the upper end of the valve has been worn away. No spur is apparent,
for it is confluent with the basi-scutal angle of the valve. The
articular ridge is very prominent, and runs down to the basi-scutal
angle; and as the valve in this part is extremely narrow, with the
spur not developed, it here assumes a channelled structure. The
basi-carinal corner of the valve is furnished with rather feeble
crests for the depressor muscles, and in those varieties in which the
basal margin is much hollowed out, this part is remarkably narrow.
_Structure of the Parietes and Radii._--The internal basal edges of
the parietes and the sutural edges of the radii and alæ, are all
smooth. The lower edge of the sheath depends freely. In the green
varieties the colour is most distinct on the internal surface of the
shell. The four compartments separate very easily when the shell has
been ill preserved in spirits, or after a very short immersion in
caustic potash.
_Mouth_, as in _E. Kingii_, excepting that there are only three teeth
on each side of the notch (which is deeper) on the labrum. The cirri
resemble those of _E. Kingii_; the segments in the sixth pair are
equally elongated, and bear five or six pairs of spines.
_Affinities._--This species is closely allied to its South American
representative _E. Kingii_; the differences consist in its smaller
size, often greenish colour, more folded walls, and narrower radii:
the internal basal edges, also, of the parietes are here smooth,
instead of being striated, as in _E. Kingii_. The terga present even
more obvious differences, in their narrowness, channelled under
surface, and in the absence of the spur, or more properly in its
confluence with the basi-scutal angle of the valve.