ely developed.

_Terga:_ these valves have a conspicuous notch to receive the apex of
the scuta; the two occludent margins either meet each other at a
rectangle, or at a much smaller angle, causing the portion thus bounded
to vary much in outline, area, and degree of prominence. This at first
led me to think that the _P. spirulae_ of Leach, in which the point is
very sharp and prominent, was a distinct species; but there are so many
intermediate forms, that the idea must be given up. I may remark, that
in all the species of Lepas, the upper part of the tergum seems
particularly variable. The degree of acumination of the basal portion of
the tergum also varies; the internal surface sometimes has small crests
radiating from the umbo.

_Carina_, broad, within deeply concave; edges sinuous, externally
sometimes strongly barbed; narrow above the fork, which latter is wider
than the widest upper part of the valve; prongs sharp, thin, diverging
at an angle of from 135 deg. to 180 deg.; the rim connecting the prongs
not, or only slightly, reflexed.

_Peduncle_, narrow, shorter than the capitulum.

_Filamentary Appendages_, none, or only one, short, obtuse projection on
each side, on the posterior face of the swelling under the first cirrus.

_Mouth._--Mandibles, with the inferior point produced into a single
pectinated tooth, rarely into two pectinated teeth; on one side of one
specimen, there were only four instead of five teeth. Palpi very narrow.
Maxillae highly variable; they may be described as formed of five steps,
of which the two lower ones are generally united into a single one,
divided by a mere trace of a notch; or with the three lower steps
blended into an irregular, projecting surface, and with even the fourth
step indistinct. I have seen these two extreme forms on opposite sides
of the mouth of the same individual,--on one side the maxillae being
regularly step-form, on the other the whole inferior part forming an
almost straight edge, standing high up above the first notch or step
which bears the two upper great spines.

_Cirri._--First pair rather far removed from the second pair, with the
longer ramus about three-fourths of the length of shorter ramus of
second cirrus; spine-bearing surfaces, hardly at all protuberant;
lateral marginal spines on the posterior cirri rather long; caudal
appendages smooth, rounded, extremely minute: penis very spinose.

_Size._--Capitulum in the largest specimen, six-tenths