The occludent segment is longer than the basal segment; it
either runs close along the orifice, or in the upper part bends inwards;
both segments are narrow, except in _D. Warwickii_, in which the basal
segment is moderately broad; the two segments are placed at an angle,
varying from 45 deg. to 90 deg., to each other. The capitulum generally
extends for a little space beneath the basal segments of the scuta, where
it contracts to form the peduncle.

The _Terga_ present singular differences in shape, and are described
under the head of each species; scarcely any point can be predicated of
them in common, except that they are flat and thin.

The _Carina_ is much bowed, narrow, and internally either slightly
concave or convex and solid; the upper end extends far up between the
terga; the lower end is formed by a rectangularly inflected, imbedded,
triangular or oblong disc, deeply notched at the end, or as in _H.
Lowei_, of a fork, the base, however, of which is wider than the rest of
the carina, so as to present some traces of the disc-like structure of
the other two species; or lastly, as in _D. orthogonia_, it terminates
in a crescent-formed cup.

_Peduncle._--This is narrow, compressed, and about as long, or twice as
long, as the capitulum; in _D. Warwickii_ it is studded with minute
beads of yellowish chitine.

_Size._--Small, with a capitulum scarcely exceeding a quarter of a inch
in length.

_Filamentary Appendages._--None. There are two small ovigerous fraena,
which, in _D. Warwickii_, had the glands collected in seven or eight
little groups on their margins.

_Mouth._--Labrum highly bullate, with small teeth on the crest; palpi
small, not thickly covered with spines. _Mandibles_ narrow, with three
or four teeth. Maxillae small, with a notch beneath the two or three
great upper spines; lower part bearing only a few pair of spines,
generally not projecting, but in _D. orthogonia_ largely projecting.
Outer maxillae, with their inner edges continuously covered with
bristles.

_Cirri._--First pair short, situated rather far from the second pair;
second pair with the anterior ramus not thicker than the posterior
ramus, and hardly more thickly clothed with spines than it, excepting
sometimes the few basal segments. All the five posterior pair of cirri
resemble each other more closely than is usual. In _D. Lowei_, the
segments of the posterior cirri bear the unusual number of eight pair of
main spines.

_Caudal