_Genus_--CORONULA.
Fig. 1, rostrum, viewed from the inner side, of _Coronula
diadema_.
_a_, sheath, marked transversely in the upper part by the
attachment of the opercular membrane.
_b_, furrow on each side of (_a_), receiving the edges of the
thick alæ of the adjoining lateral compartments.
_c′′_, special plate, on which the alæ on their outer sides
rest.
_d_, radius, on the edge it may be just seen to consist of an
outer layer (the normal radius), and a much thicker inner
part (the pseudo or complementary radius) formed of oblique
denticulated septa.
_e e′ e′′_, basal edge of wall, which from its commencement
at _e_, or _e′′_ can be followed, folding up to near the
basal edge of the sheath, to its termination at _e′′_ or
_e_.
_f_, serrated lines of junction between the folds of the wall.
2, Lateral compartment of _C. diadema_, seen laterally, on a
smaller scale than last fig., but taken from the same
shell; letters of reference the same: this figure, if the
ala _a′_ were removed, would do for a lateral view of the
rostrum, or fig. 1.
_a_, sheath, much foreshortened.
_a′_, ala (therefore also part of sheath), and the edge of
which fits into _b_ of fig. 1.
_b_, furrow receiving edge of ala of the adjoining
carino-lateral compartment.
_c′′_, special plate, seen edgeways.
_d_, radius, the division into two parts, viz., the thin
outer normal radius, and the under pseudo or complementary
radius here shown (rather exaggerated) plainer than in fig.
1.
_e_, basal edge of wall; to the right hand the three folds at
their inner ends are seen obliquely, one behind the other:
these are seen directly in front in fig. 1.
3, lateral compartment of _C. balænaris_, seen laterally;
letters of reference the same as in last fig., but _c′′_
not introduced for this plate is barely developed, and
only in the lower part, and is attached to the radius: _g
g_ points where fresh folds have been formed in the walls
along the lines of suture, as may be seen in the outline of
the wall in fig. 5.
4, lateral compartment of _C. reginæ_, seen laterally; letters
of reference the same as in the last two figures.
5, Coronula balænaris, outline of the basal margin of the
folded walls: _s_, _s_, the six sutures. The wall can be
continuously followed from one end of a suture to the next
suture.
6, Coronula diadema; small portion of the external surface of
the wall, close to the basal edge, highly magnified; _a_,
outer lamina, not extending down to the basal edge; _b_,
inner lamina; _c_, projecting longitudinal septa.
7, Coronula diadema; transverse section through the upper part
of the shell, showing the rostrum and the two adjoining
lateral compartments (and the alæ of the carino-lateral
compartments), all supposed to be a little separated from
each other, so that the sutures, _s s_, are shown by white
lines.
A A A, rostrum.
C C, lateral compartments.
D D, carino-lateral compartments, of which only the alæ
(_a′_) are shown.
Of the letters in italics, those which occur in figs. 1, 2, 3,
4, 5, refer all to the same parts, viz.:--
_a_, sheath, continuous with (_a′_) the alæ, where such occur.
_c′′_, special plate on which the alæ rest.
_d_, radius, divided into a thin outer normal radius, and the
inner complementary portion, the latter shaded by convex
lines of growth.
_d′_ is a special tube (seen only as a black dot) for a
thread of corium.
_e_, folded walls.
_f_, junction of the folded walls (see _f_, in fig. 1)
leading into the cavities (_f′_) open beneath, and filled
up by the epidermis (see Pl. 15, fig. 4) of the whale.
_h_, inside of the transverse loops of wall, occupied by
corium: in the enlarged section of a loop, in C. balænaris,
in Pl. 15, fig. 2 _a_, the opposed sides are seen to be
connected by shelly longitudinal plates.
_v_, cavity occupied by the ovarian tubes and cæca.