her there were
about eighty valves; in medium-sized specimens, the number is about the
same as in _P. cornucopia_. The upper latus, (viewed internally,) has an
area about twice as large as that latus, which corresponds to the
interspace between the carina and terga; whereas in _P. cornucopia_ the
upper latus is only slightly larger than this same valve. The apex of
the basal internal margin of the carina is here rounded, instead of
being square, as is generally the case with _P. cornucopia_. The strong
membranous margin of the orifice of the sack, in its upper part, is
almost one third as wide as the widest part of the terga, whereas in _P.
cornucopia_ it is only one fourth of this same width. The peduncle
apparently is rather longer, compared with _P. cornucopia_, and the
calcareous scales on it perhaps a little larger in proportion.

In a very young specimen, with the capitulum barely exceeding 1/20th of
an inch in length, I could distinguish the sub-rostrum, sub-carina, the
upper, and some of the lower latera.

_Filamentary Appendages._--These, in a medium-sized specimen, are
arranged on the prosoma in four longitudinal approximate rows, there
being twelve in each row; those in the two outer rows are only half the
length of those in the two inner rows; those nearest the thorax are the
longest; there are some papillae outside the outer rows. In a very large
specimen with its capitulum 1.3 in length, these filaments were very
much more numerous, and some were placed on the first segment of the
thorax, and at the bases of several of the posterior cirri. Some of the
filaments are bifid, trifid, and even branched. In all the specimens, at
the bases of the first pair of cirri, there are, on each side, a pair of
filaments, (one below the other,) pointing upwards, less than half as
long as those on the prosoma: also on each side of the mouth, there is a
longer and thicker filament, pointing upwards, with a few very minute
scattered spines on it; the apices of these three pair of filaments, as
well as of some of the others, are roughened with very minute pectinated
scales. All these filaments were gorged with the branching testes.

_Mouth._--The parts are closely similar to those in _P. cornucopia_; in
the mandibles, the interspace between the third tooth and the inferior
angle, is slightly pectinated: in the maxillae, there are six or eight
pairs of spines between the two upper tufts of fine spines.

_Cirri._--These are i