three fourths of the length of the scuta; neither the upper nor lower
point much acuminated. All the valves most imperfectly calcified: in one
specimen, the scutum on one side was simply horny, without a particle of
calcareous matter. The summit of the capitulum nearly intermediate in
outline between the common square, and bluntly-pointed form of _var.
chelonophilus_. I compared the cirri and trophi with those of a common
variety, and could detect not the smallest difference. This variety
differs from _var. Olfersii_, in the less development of its carina, and
from _chelonophilus_, in the greater development of its carina, and
especially of its terga. It would appear as if the great variability of
the valves was connected with the absence of calcareous matter.

3. CONCHODERMA HUNTERI. Pl. III, fig. 3.

CINERAS HUNTERI. _R. Owen._ Cat. Mus. Coll. of Surgeons, (1830),
Invert. Part I., p. 71.

_C. valvis angustis: scutis trilobatis, prominentia laterali non latiore
quam inferior: tergorum parte superiore paene rectangule secundum
aperturae marginem flexa: carina valde arcuata: pedunculo brevi, in
capitulum coalescente._

Valves, narrow: scuta, trilobed, with the lateral lobe not wider than
the lower one: terga, with the upper part bent almost rectangularly
along the margin of the orifice: carina considerably arched: peduncle
short, blending into the capitulum.

No filament attached to the pedicel of the second cirrus.

_Var._--Carina absent; scuta, with the upper lobe absent; terga, with
the rectangular projection little developed.

Attached to the skin of a snake, probably the Hydeus or Pelamis
bicolor, and therefore from the tropical Indian or Pacific
Oceans. Mus. Coll. of Surgeons.[40]

[40] I owe to the kindness of Professor Owen, an examination of
these specimens, and information regarding them.

_Capitulum_, with the membrane very thin; summit obtusely pointed.
Valves linear and thin.

_Scuta_, elongated, flat, with the upper projecting lobe rather more
acuminated than the lower, and equalling it in length; lateral lobe not
wider than the lower, and about as long as it, forming an angle of about
55 deg. with the upper one.

_Terga_, of somewhat variable length, generally about half as long as
the carina, narrow, and of nearly equal width throughout; lower point
sharp; externally convex; internally solid, with a trace of a central
depressed line; the upper fourth part gener