the crest. Palpi small, with few bristles. _Mandibles_, with
the whole inferior part, very narrow; three teeth very sharp, with a
slight projection, perhaps, marking the place of a fourth tooth;
inferior angle ending in the minutest point; first tooth as far from the
second, as the latter from the inferior angle. _Maxillae_ with a _broad_
shallow notch; inferior angle much rounded, bearing only four or five
pair of spines.

_Cirri._--First pair apparently remote from the second pair; all five
posterior pair lost; first pair short, with the rami unequal by about
two segments; segments clothed with several transverse rows of bristles;
terminal segments blunt.

3. DICHELASPIS PELLUCIDA. Pl. II, fig. 7.

_D. valvarum singularum acuminibus superioribus et inferioribus vix
intersecantibus: scutorum segmento basali multo angustiore quam
segmentum occludens; longitudine fere dimidia: tergis bipenniformibus,
margine integro, manubrii acumine ad carinam flexo._

Valves with the upper and lower points of the several valves only just
crossing each other. Scuta with the basal segment much narrower than the
occludent segment, and about half as long as it. Terga like a
battle-axe, with the edge smooth, and the point of the handle bent
towards the carina.

Mandibles with four teeth; caudal appendages twice as long as the
pedicels of the sixth cirrus.

Indian Ocean; attached to a sea-snake.

This species comes very close to the _D. Grayii_, which likewise was
attached to a snake; but I cannot persuade myself, without seeing a
graduated series, that the differences immediately to be pointed out can
be due to ordinary variation. I am much indebted for specimens to the
kindness of Mr. Busk.

_General Appearance._--The membrane of the capitulum and peduncle is
surprisingly thin and pellucid, so that the ovarian tubes within the
peduncle can be traced with the greatest ease. The valves are small, the
apices only just crossing each other, and are composed of yellow
chitine, with mere traces of calcification. The capitulum is pointed,
oval, .15 of an inch long; the peduncle is narrow, and fully twice as
long as the capitulum.

_Scuta._--The two segments stand at right-angles to each other; the
basal segment is linear and pointed, fully half as long, but only one
third as wide, as the occludent segment. The point of junction of the
two segments is wider than the rest of the basal segment. This latter
segment lies some little w