CORONULITES DIADEMA (?) _Parkinson_, Organic Remains (1811), vol. 3,
p. 240, Pl. 16, fig. 19.
_Shell (probably) crown-shaped, with longitudinal convex ribs, having
their edges crenated, and their surfaces rugged, both externally and
internally, with transverse ridges: radii moderately thick; the spaces
between the radii and the alæ solidly filled up._
_Fossil_ in Red Crag, (Bawdsey and Sutton); Mus. S. Wood and
Geological Society.
The species here described, though near to _C. diadema_ and easily
confounded with it, I have no doubt is distinct. I owe to the kindness
of the Rev. Mr. Image an examination of the original specimen figured
by Parkinson; and in Mr. Stutchbury's collection there is a similar and
more perfect specimen; both of these resemble _C. diadema_ in general
form, but have been too much worn to be positively identified. The
following description is drawn up from some compartments collected by
Mr. Searles Wood, belonging certainly to three, and probably to four
individuals, one of which was young; as these specimens agree in all
essential respects, I feel pretty confident that the characters, by
which the present species differs from _C. diadema_, are of specific
value.
_Structure of Shell._--The longitudinal ribs on each compartment
(_i. e._ the terminal transverse loops), are convex and prominent,
as in _C. diadema_, but they are crossed by more prominent ridges
of growth than even in the roughest varieties of that species, so
that the surface of the shell is more rugged. In the three previous
species, the surface of the wall entirely round the cavities occupied
by the whale's skin, is striated only by longitudinal very fine
lines; but here, the outer portion, or that (fig. 6) formed by each
transverse loop, is crossed by transverse ridges of growth, like,
but less prominent than, those on the external surface of the shell.
The minute teeth, along the lines of junction between the transverse
loops, are here less regular, and can hardly be said to exist; for
the two edges are locked together by what may be more strictly
called minute zig-zag ridges than teeth. The exact number of the
circumferential plications in the walls is variable in the same
manner as in the three foregoing species. The sutural edges of the
radii are about as thick as, or rather thicker than, in _C. diadema_.
As in this latter species, and in _C. reginæ_, each ala rests, not
on the internal surface (as in _C. balænaris_, and in all other
Balanidæ) of the radius, but on a special plate; but in _C. barbara_,
instead of a deep chamber, running up to the apex of the compartment,
being left between the radius and ala, this part is filled up almost
entirely by solid shell. Although the extent to which this chamber is
filled up varies a little, and although its depth varies a little in
_C. diadema_, yet there is a marked difference between the specimens
of this latter species, in which the chamber is most filled up, and
those of _C. barbara_, in which it is least filled up. The alæ are
thick, as in _C. diadema_, and their sutural edges have a central
ridge, sending off on both sides sinuous ridges. The basal margins
of the alæ are not short compared with their upper margins, and
therefore the whole ala is not wedge-formed; and in this rather
important respect _C. barbara_ resembles _C. balænaris_ (Pl. 16,
fig. 3), and differs from _C. diadema_ (fig. 2). The lower edge of
the sheath does not seem to have projected freely,--in this respect,
also, resembling _C. balænaris_. From the basal margin of the alæ not
being narrow, and from the inner ends of the folded walls being, as
it would appear, also broad, I have little doubt that the cavity in
which the animal's body was lodged, resembled in shape that in _C.
balænaris_, the membranous basis being larger than the orifice of the
shell.
Opercular valves unknown.
_Summary._--This species is more nearly related to _C. diadema_ than
to the others; but in some points, just specified, it resembles _C.
balænaris_. The characters by which it differs from all the species
are, firstly, the more prominent transverse ridges on the external
surface of the shell, and more especially on the surfaces bounding
the outer sides of the cavities occupied by the epidermis of the
whale. Secondly, the character of the teeth, or rather ridges, along
the lines of junction between the transverse loops. And, thirdly, the
spaces between the radii and the plates on which the alæ rest, being
solidly filled up.
_Species Dubiæ._
The _Coronula bifida_ is an Italian tertiary species, so named by
Bronn, in his "Italiens Tertiär-Gebilde" (1831), p. 126. It is very
possible that this may be identical with _C. barbara_, but Bronn does
not seem to have been aware of the absolute necessity of giving minute
details in his descriptions of fossil cirripedes. The chief character
of _C. bifida_ is thus given:--"Eine tiefe Furche oder Spalte theilt
die Längenrippe von oben herab bis zur Hälfte, welche bei der sonst
ähnlichen _C. diadema_ entweder ganz fehlt, oder nur zuweilen kurz
angedeutet ist." Had it been stated that the longitudinal ribs were
divided from the middle down to the base, instead of from the top to
the middle, the description would have been intelligible to me, though
the character thus afforded would not have been of specific value, as
this dividing of the ribs occasionally occurs in all four species, and
is produced by the formation of new folds to the walls.