asal segments (5/13ths of the whole number in the second cirrus, and
5/14ths in the third cirrus) of their anterior rami, extremely broad,
protuberant, and paved with serrated bristles, amongst which, (except on
the actual lowest segment,) there are some simply pectinated spines, and
others with their teeth elbowed, exactly as in the first cirrus. The
basal segments of the posterior rami of the second and third cirri,
differ from the three posterior cirri only in the spines being slightly
more numerous; but none of them are pectinated.

_Pedicels_, rather short; the upper segment resembles, in the
arrangement of its spines, the segments of the posterior cirri; the
lower segment is longer than the upper, and has _two_ tufts of fine
spines, between the two rows of long spines. In the second and third
cirri, these two intermediate tufts on the lower segment of the pedicel,
are not so distinctly separated from each other.

_Caudal Appendages_, very small, uniarticulate, blunt and rounded; tips
bearing a few, very short, thick spines.

_Alimentary Canal._--OEsophagus, somewhat curved at the lower end, where
it enters the stomach, which has no caeca; rectum, unusually short,
extending from the anus only to the base of the fifth pair of cirri.
Within the stomach, from top to bottom, there were thousands of a
bivalve entomostracous crustacean.

_Generative System._--Both ovaria and testes are largely developed; the
former fill the long peduncle; the testes enter both the pedicels of the
cirri, and the filamentary appendages on the prosoma; vesiculae seminales
very large, reflected at their ends, extending across each side of the
stomach. Penis rather small, coloured purplish, with numerous little
tufts of bristles.

_Variation._--In some specimens in the British Museum, collected by Sir
J. Ross, in the Southern ocean, and in another older set from an unknown
source, several parts of the outer tunic of the animal's body presented
the remarkable fact of being calcified, but to a variable degree;
whereas in several specimens from California, there was no vestige of
this encasement. Considering it most improbable that the calcification
of the integuments should be a variable character, I most carefully
compared the above-mentioned sets of specimens, valve by valve, trophi
by trophi, and cirri by cirri, and found no other difference of any
kind; therefore I cannot hesitate to consider both to be the same
species. The first Sout