some fine muscles attached to the membrane
forming the supra-oesophageal cavity. The trophi serve merely for the
prehension of prey, and not for mastication.

The _Labrum_, as stated, is always bullate or swollen; and sometimes the
upper exterior part forms, as in Ibla (Pl. IV, fig. 8 _a_, _c_), and
Dichelaspis, an overhanging blunt point. The object, I suspect, of this
bullate form is to give, in the upper part, attachment to longer muscles
running to the lateral surfaces of the mandibles, and lower down to the
oesophagus. The crest close over the supra-oesophageal cavity, is
generally furnished with small, often bead-like teeth. The _Palpi_ are
small, their apices never actually touching each other; they are more or
less blunt, not differing much in shape in the different genera (Pl. X,
figs. 6 to 8), and clothed with spines. They are not capable of
movement; their function seems to be to prevent prey, brought by the
cirri, escaping over the labrum; I infer this from finding in Anelasma
and in the male of Ibla, which have the cirri functionless, that the
palpi are rudimentary.

The _Mandibles_ (Pl. X, figs. 1-5) have from two to ten strong teeth in
a single row; where the number exceeds five, several of the teeth are
small; the inferior angle is generally pectinated with fine spines; in
Lithotrya (fig. 2), the interspaces between the teeth are also
pectinated. In the same individual there is not unfrequently one tooth,
more or less, on opposite sides of the mouth. Internally, the mandibles
are furnished on their outer and inner sides with several ligamentous
apodemes, in Lithotrya roughened with points (Pl. X, fig. 2), for the
attachment of the muscles; of these (fig. 1), there is a chief depressor
and elevator, attached at their lower ends to near the basal fold of the
mouth, and a lateral muscle, attached to the broad basal end of the
palpi, and serving, apparently, to oppose the edge of mandible to
mandible. The _Maxillae_ in the different genera (Pl. X, figs. 9 to 15)
differ considerably in outline; they are generally about half the size
of the mandibles; at the upper corner, there are always two or three
spines larger than the others, and often separated from them by a notch;
the rest of the spinose edge is straight, or irregular, or step-formed,
or with the lowest part projecting, or with one or two narrow
prominences bearing fine spines. All these spines, quite differently
from the teeth of the mandibles, are