once
dried. I was able to distinguish that the two lower pair of spines on
the ventral surface, are seated a little way one below and within the
other, as in _S. vulgare_. The abdominal spines altogether form quite a
brush, and there are certainly several more than in _S. vulgare_, and
those on the two sides are much longer.

_Antennae._--The disc is hoof-like, with the upper surface forming a
straight line with the upper edge of the basal segment; the apex is
pointed and clothed with some fine down; there is a single spine
pointing backwards, which rises from the lower flat surface. The
ultimate segment was hidden in laminae of cement; and I was not able to
make out its structure. There is a single spine on the outer edge of the
basal segment, in the usual position. The entire length of the limb,
measured from the end of the disc to the further margin of the basal
articulation, is 36/6000ths of an inch; measured to the inner margin, it
is; 21/6000ths of an inch; the disc itself is 12/6000ths of an inch
long; these measurements differ a little both absolutely ad
proportionally, compared with those of the antennae of _S. vulgare_.

_Cavities in the Scuta of the Female for the reception of the
Males._--These extend nearly parallel to the tergal margin, transversely
across the valves, for three fourths of their width; they are seated
above the depression for the adductor muscle, and are more conspicuous
than it; they are deep and well defined, and each exactly contains one
male. The males are placed with their orifices in a little notch in the
occludent margin, and their prehensile antennae at the further end. The
distance to which the cavities extend across the valve, and their
distance from the upper or tergal margin, varies a little, but chiefly
in accordance with the age of the specimens; for the valve continues to
increase in width, whilst the size of the cavity remains the same. The
occludent margin of the scutum in the largest female, was .1 of an inch
in length; of another, in which there was a fully developed cavity,
.084; of a third, in which there was no cavity, only a slight concavity,
with a preparatory impression, the length of the occludent margin was
.062. The larger and smaller of these three valves, are drawn of their
proper proportional sizes, in Pl. VI, figs. 1 _b'_, 1 _c'_. The
preparatory impression (fig. 1 _c'_, _b_), consists of a narrow, not
quite straight, extremely slight furrow, of slightly irr