under side of the basal
segment, there is, on each valve, a longitudinal calcified fold, serving
as a tooth.

_Terga_ broad, with a deep notch corresponding to the apex of the
occludent segment of the scuta; the part beneath the notch is of nearly
the same width throughout, and is twice as broad as the occludent
segment of the scuta; it has its basal angle very broad and blunt. The
entire length of the terga equals two thirds of that of the occludent
segment of the scuta; occludent margin simply and slightly curved.

The _Carina_ is of nearly the same width throughout, with the upper part
rather the widest, and the apex blunt; within _convex_; it extends up
between three fourths of the length of the terga, terminating downwards
in a fork with very sharp prongs, standing at right-angles to each other
(fig. 8 _a_.) The fork, measured from point to point, is thrice as wide
as, and measured across at the bottom of the prongs it is wider than,
the widest upper part of the valve,--a resemblance being thus shown with
the triangular notched disc in _D. Grayii_. The points of the prong
extend under about one fourth of the length of the basal segments of the
scuta.

_Peduncle_ rather longer than the capitulum, which, in the largest
specimen, was 2/10ths of an inch in length; peduncle narrow, close under
the capitulum; membrane thin and structureless. The larger specimen had
almost mature ova in the lamellae.

_Mouth._--Labrum with a few bead-like teeth on the crest, distant from
each other even in the central part; palpi rather small, moderately
clothed with bristles.

_Mandibles_, with four teeth; the inferior angle blunt and broad,
showing, apparently, a rudiment of a fifth tooth; the first tooth is as
far from the second, as is this from the inferior angle; second, third,
and fourth teeth very blunt, whole inferior part of mandible not much
narrowed. Maxillae small, with a small notch under the three upper
spines, which are followed by five or six pair, nearly as large as the
upper spines.

_Cirri._--First pair remote from the second; their rami nearly equal,
and about one third of the length of the rami of the second cirrus;
thickly clothed with bristles: rami of the second cirrus of equal
thickness, but little shorter than those of the sixth cirrus; the three
or four basal segments of the anterior ramus are thickly clothed with
spines; the other segments, and all the segments on the third pair,
resemble the segments