Appendages._--Uni-articulate, spinose; in D. pellucida they are
twice as long as the pedicels of the sixth cirrus, but I could not
perceive in them any distinct articulations.

_Distribution._--Attached to crabs at Madeira, and off Borneo;
to sea-snakes in the Indian Ocean. The individuals of all the
species appear to be rare.

_General Remarks._--Four of the five species, forming this genus, though
certainly distinct, are closely allied. I have already shown, that
although the characters separating Lepas, Paecilasma, and Dichelaspis are
not very important, yet if they be neglected these three natural little
groups must be confounded together. Dichelaspis is much more closely
united to Paecilasma than to Lepas, and, as far as the more important
characters of the animal's body are concerned, there is no important
difference between them. Consequently, I at first united Paecilasma and
Dichelaspis, but the latter forms so natural a genus, and is so easily
distinguished externally, that I have thought it a pity to sacrifice it.
The carina, (which seems to afford better characters than the other
valves in Dichelaspis,) from generally running up between the terga and
in ending downwards, in three of the species, in a deeply notched disc
or fork, more resembles that in Lepas than in Paecilasma; in the manner,
however, in which the imbedded disc, in _D. Warwickii_ and _D. Grayii_,
nearly cuts off the inside of the capitulum from the peduncle, there is
a resemblance to _Paecilasma eburnea_. In the extent to which the valves
are separated from each other, in the bilobed form of the scuta, (the
two segments in Dichelaspis, perhaps, answering to the upper and lateral
projections in the scuta of _Conchoderma virgata_,) and in the basal
half of the scuta not descending to the base of the capitulum, there is
a considerable resemblance to Conchoderma; in both genera the adductor
muscle is attached under the umbones of the scuta; but the structure of
the mouth and cirri and caudal appendages shows that the affinity is not
stronger to Conchoderma than to Lepas. It appears at first probable,
that Dichelaspis would present a much closer affinity to _Paecilasma
fissa_, in which, owing to the scuta being formed of two segments, there
are seven valves, than to any other species of that genus; but in _P.
fissa_ the primordial valve is triangular and is situated on the basal
segment, whereas, in Dichelaspis, it is elliptic and is s