f bead-like
teeth along the basal margins of the scuta. The ridges vary much,
sometimes alternately wide and narrow; in two specimens of equal size,
there were, in one, thirty-two ridges, and in the other only eighteen,
on the scutum.

_Scuta_, with the occludent margin rounded and protuberant to a variable
degree, but always leaving a rather wide space between the margin, and
the ridge which runs from the umbo to the apex; apex pointed. Right-hand
internal tooth considerably larger than that on the left, which is often
reduced to a mere ridge; internal basal rim thick, sometimes furrowed
along its upper edge, but of variable thickness, sometimes not extending
as far as the baso-carinal angle. _Terga_, sometimes equalling,
sometimes only two-thirds of, the length of the scuta; in young
specimens, the two occludent margins form a right-angle with each other;
in older specimens they form less than a right-angle, and hence the
portion of valve thus bounded is unusually protuberant. _Carina_, within
deeply concave; exterior sides finely furrowed longitudinally, generally
denticulated; valve only slightly narrowed in above the fork, of which
the prongs diverge at an angle of 90 deg., or rather more, and are wider
than the widest upper part of the valve; rim between the prongs
reflexed; the heel or external angle, just above the fork, sometimes
considerably prominent. I have seen only a single large specimen with
its carina barbed. In half-grown specimens, (var. _dilatata_, Leach,)
the carina is often strongly barbed, with the upper point much
acuminated, the fork about twice as wide as the widest upper part, and
the prongs diverging at rather more than a right-angle. In some
specimens, especially very young ones, there are at the base of the
carina, above the fork, some strong, downward-pointed, inwardly-hooked,
calcareous teeth; such occur also in some specimens along the basal
margins of the scuta, two of these hooked teeth under the umbones of the
scuta being larger than the rest: specimens conspicuously thus
characterised came from the Navigator Islands; in these, I may add, the
acutely triangular primordial valves were quite plain.

_Peduncle_, generally about as long as the capitulum; in young specimens
generally short.

_Filamentary Appendages_, generally five, sometimes six, on each side;
one is seated on the side of the prosoma, and the four others placed in
pairs beneath the basal articulation of the first cirru