_Shell globulo-conical or depressed, with longitudinal, much flattened
ribs, having their edges crenated, and their surfaces striated and
granulated; orifice hexagonal: radii thin, not exceeding one fifth of
the thickness of a compartment: terga absent._
_Hab._--Attached to whales, Pacific Ocean; Mus. Cuming, Stutchbury,
and Darwin.
I have seen eight specimens of this form--two in Mr. Cuming's
collection, one of which was procured at Iquique in Peru, the other
from an unknown locality; one was given me in Chile, and was stated
to have come from the Pacific; two others are in Mr. Stutchbury's
collection, from unknown but distinct localities, and three in a
group in the British Museum. These eight specimens, of which six were
collected separately, all strikingly agree in general aspect and in
details of structure, so that I can easily recognise the shell, and can
at once pick out a single compartment, when mingled with those of the
two foregoing species; nevertheless, the differences are so small, that
I at first hesitated whether to name the species; but, upon reflection,
I am convinced that it is distinct. _Coronula reginæ_ is much more
closely related to _C. diadema_ than to _C. balænaris_, and I suspect
that it replaces in the Pacific the former of these two species.
_General Appearance_; shell conical, straight-sided; some specimens
being nearly as much depressed as _C. balænaris_, and considerably
more depressed than any variety of _C. diadema_; other specimens
being globulo-conical, but rather less globular than the ordinary
form of _C. diadema_. I may here remark, that shape is of more value
in this genus, in which the shell is attached to the yielding skin
of whales, than in those genera in which it adheres to rocks. The
orifice is neatly hexagonal, and the whole internal cavity, when the
opercular membrane is removed, can be seen from one point of view,
owing to the contraction of the lower part of the cavity and small
size of the basal membrane. The surface of the shell is smooth, but
has, even up to the summit, a peculiar frosted appearance, different
from that of the foregoing species, caused by the longitudinal
striæ being rather more distinct, and being crossed by beaded, very
delicate transverse lines of growth. The ends of the transverse
loops, forming the exterior surfaces of the compartments, are much
flattened, even more so than in _C. balænaris_. The lines of junction
between the loops, are finely serrated, as in _C. diadema_; and
internally they are solidly filled up, instead of being formed into a
set of tubes by longitudinal septa, as in _C. balænaris_. The under
side of the shell, with its folded walls, presents an appearance
intermediate between the variable appearance of this part in the
above two species.
The sutural edges of the radii (Pl. 16, fig. 4) offer by far the
most remarkable character, in their thinness from top to bottom; for
they hardly exceed one fifth of the thickness of the compartment,
measured from the external surface to the base of the sheath; hence
a very large cavity is left between the radii and alæ: in the
thickness of the radii the three species already described form a
series, _C. reginæ_ at one end and _C. balænaris_ at the other. The
sinuous plates, forming the lower part of the radius, are coarser and
stand rather further apart than in _C. diadema_. The alæ are thick,
and have the same outline, being narrow at their basal margins and
broad at top, as in _C. diadema_, with their sutural edges similarly
constructed: the basal edge of the sheath likewise projects freely.
_Operculum._--This resembles most closely that of _C. diadema_. There
are no rudiments of terga. The scuta cannot be distinguished from
those of _C. diadema_.
_Mouth._--The labrum has a row of inwardly curved little teeth along
the whole crest, and these I did not notice in _C. diadema_: there
is only a trace of the prominence on the outside at the bottom of
the central notch. The hairs on the basal exterior margin of the
palpi are moderately long. The mandibles have five teeth. In the
_Cirri_, the first pair resembles in its peculiar structure those of
_C. diadema_. In the sixth pair, however, the segments support only
three pairs of main spines: but the specimen was not very large, and
probably in old specimens there would have been four pairs.
_Summary._--The present species differs from both the foregoing
only in its rather more conical and straight-sided outline, smooth,
frosted surface, and in the narrowness of the sutural edges of the
radii, and consequent large size of the chambers between the radii
and alæ. It resembles _C. diadema_, as far as the shell is concerned,
in the external ribs or transverse loops having their lines of
junction serrated and in being solidly filled up--in the shape of
the orifice and of the internal cavity of the shell--in the shape
and structure of the alæ--and in the basal edge of the sheath being
free. It comes nearer to _C. diadema_ than to _C. balænaris_ in the
structure of the radii. It differs from _C. diadema_, and comes
nearer to _C. balænaris_, in the external ribs being flattened,
instead of being convex, and in the lines of growth being very
delicate. But as it resembles _C. diadema_ in the several foregoing
characters of its shell, in the opercular valves, in all parts of the
mouth (excepting the labrum), and in the cirri, it is very much more
nearly related to that species than to _C. balænaris_.