up.

Mandibles, with three or four teeth; maxillae notched, with the lower
part of edge generally not prominent; anterior ramus of the second
cirrus not thicker than the posterior ramus, not very thickly clothed
with spines; caudal appendages uniarticulate, spinose.

_Distribution._--Eastern and Western warmer oceans in the
Northern hemisphere, attached to crustacea, sea-snakes, &c.

_Description._--The capitulum appears to contain seven valves; but, on
examination, it is found that two of the valves on each side, are merely
segments of the scutum; these are united at the umbo, in three of the
species, by a narrow, non-calcified portion of valve, where the
primordial valve is situated; in _D. orthogonia_, however, the junction
of the two segments is perfectly calcified, and of the same width as the
whole of the basal segment. The capitulum is much compressed, broad at
the base, and extends a little beneath the basal segments of the scuta.
The valves are very thin, often imperfectly calcified, and generally
covered with membrane. They are not placed very close together, and in
all the species a considerable interspace is left between the carina and
the two other valves: in the _D. Grayii_ the valves are so narrow that
they form merely a calcified border round the capitulum. The membrane
between the valves and over them, is very thin, and is thickly studded,
in some of the species, with minute blunt conical points, apparently
representing spines. The valves in the same species present considerable
variations in shape; in their manner or direction of growth, and in the
position of their primordial valves, they agree with Lepas and
Paecilasma.

_Scuta._--In three of the species the two segments, named the occludent
and basal, appear like separate valves, but these, by dissection, can be
most distinctly seen to be united at the rostral angle. The primordial
valve, formed of the usual hexagonal tissue, is elliptic, elongated, and
placed in the direction of the occludent segment; calcification
commences at its upper point, so as to form the occludent segment, and
afterwards at its lower point, but rectangularly outwards, to form the
basal segment; in the minute space between these two points of the
primordial valve, there is, in four of the species, no calcification; so
that the two segments are united by what may be called a flexible hinge;
in _D. orthogonia_ the two calcareous segments are absolutely
continuous.