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.