h, and therefore, situated at variable
distances from each other, but always remote and imbedded in membrane.

_Scuta_, trilobed, consisting of an upper and lower lobe (the latter
generally the broadest), united into a straight flat disc, with a third
lobe standing out from the middle of the exterior margin, generally at
an angle of from 50 deg. to 70 deg. (rarely at right angles) to the upper
part, and generally (but not always) bending a little inwards. The shape
of the lateral lobe varies from rounded oblong to an equilateral triangle;
as it approaches this latter form, it becomes much wider than the upper
or lower lobes. In one specimen, and only on one side, the scutum (fig.
2 _d_) presented five points or projections. In some specimens, the
scuta are very imperfectly calcified, and consist of several quite
separate beads of calcareous matter of irregular shape, held together by
tough brown membrane.

_Terga_, extremely variable in shape, placed at nearly right angles to
the scuta: beyond their carinal ends (fig. 2 _b_), the capitulum
presents two small prominences, which are important as indicating the
position of the homologous, ear-like appendages in _C. aurita_.[39] The
upper ends of the terga are imbedded in membrane, and project freely
like little horns for about one third of their length: this free portion
exactly answers to the projecting portion, bounded by the two occludent
margins, in the terga of Lepas. The freely projecting portion is
generally curled inwards, and the carinal portion more or less
outwards,--the form of the letter =S= being thus approached; but the
curvatures are not exactly in the same plane. The whole valve is
generally of nearly equal width throughout, the carinal part being a
very little (but in some specimens considerably) wider; internally, it
is deeply concave; both points generally are blunt and rounded. In some
rare varieties (_Cineras chelonophilus_ of Leach, fig. 2 _c_), the terga
are much smaller and flat, with both points sharp, the whole upper
portion being much and abruptly attenuated, and internally, without a
trace of a concavity. Generally, the terga are about two thirds of the
length of the scuta, rarely only half their length; generally, they are
separated from the apices of the scuta by about their own length, rarely
by twice their own length. Generally, the terga are shorter than the
carina, but sometimes a very little longer than it: generally they are
distant by