---- LYONSII. G. B. Sowerby. Genera of Recent and Fossil Shells, Plate, 1823, (sine descript.)
[112] The synonymy of this species is complicated. De Blainville gives no description under the article Conia, published in 1818, or in the vol. published in 1822; but I believe, from the figures of the opercular valves, that I have correctly identified this species with his C. radiata. Mr. Sowerby gives no description of C. Lyonsii, or any figure of the opercular valves, but his drawing of the shell is much better than de Blainville’s, and I believe it is the same species. Whether de Blainville’s or Sowerby’s plate appeared first I cannot ascertain. In the second edition of Lamarck, Conia radiata of Blainville is given as a synonym to Balanus radiatus of that work; but this is quite erroneous. I may add that if de Blainville’s name does not apply to the present species, it must to [T. cœrulescens], and as the latter is the older name it will be permanent. In this case, [T. radiata] might be allowed to stand as my own name, considering that Mr. Sowerby’s figure is imperfect and is not accompanied by any description. At first I thought that the present species might be the Lepas mitra of Spengler, (‘Skrivter af Naturhist. Selskabet,’ 1790, Tab. 6, fig. 5), but the parietes are not described as porose; and the folds on the walls are too broad; on the other hand, his description of the opercular valves makes me think this may be the same species.
Shell white, with numerous approximate longitudinal ribs: radii broad, with their summits slightly oblique, internally porose: tergum with the articular ridge extraordinarily prominent, with the spur not joined to the basi-scutal angle.
Hab.—West Indies, adhering to [Balanus eburneus] and to Lepas anserifera. New South Wales, adhering to [Tetraclita porosa]. Attached to [Balanus tintinnabulum], on a ship’s bottom from Sumatra; not rarely attached to Balanus tintinnabulum on ships’ bottoms; Mus. Brit., Stutchbury, and Cuming.
General Appearance.—Shell white, rather steeply conical, with numerous, approximate, rather narrow, longitudinal, rounded ribs on the walls: in a specimen half an inch in diameter, there were from eight to twelve ribs on each compartment. The outer lamina of shell seems always well preserved. Orifice rounded, trigonal. Radii white, smooth, broad, with their summits only slightly oblique. I have seen one specimen 1.2 in basal diameter, but quarter of an inch is a common size, and very young specimens are unusually frequent in collections.
Scuta broad, externally not striated longitudinally. The articular ridge is prominent, and the furrow deep, but not in so great a degree as in [T. cœrulescens]. The adductor ridge is only slightly prominent; it extends upwards only a little way above the lower end of the articular ridge, and does not form with the latter a cavity. There are no crests for the rostral depressor muscle, but there is a little pit, formed by the folding over of the occludent margin.
Terga.—These valves, when articulated with the scuta (fig. [5 b]), project above them to an extraordinary degree, and are separated from them by a deep, fissure-like hollow, caused by the remarkable prominence of the articular ridge of the terga. The upper part of the tergum is not beaked, and does not project freely much above the sack. The valve is large; externally there is a rounded longitudinal furrow. The tergal margin is broadly inflected. The articular furrow is deep, and the articular ridge far more prominent than in any other sessile cirripede, for it projects, as measured from the outside surface, more than half the width of the valve; and consequently the valve, when viewed vertically from above, almost appears as if formed by the union of three plates, viz., the articular ridge, and the outside surface on each side of the spur. The spur is of moderate width, with the corners rounded: it is placed near, but not close to the basi-scutal angle, so that there is on this side a small portion of basal margin, forming nearly a straight line with the margin on the carinal side. In some young specimens, about the tenth of an inch in diameter, from the West Indies and from New South Wales, the spur (the position of which I found varied a little in some other specimens) was placed nearly in the middle of the valve, and very nearly at right angles to the basal margin; it is possible that these may be a distinct species, but without larger specimens to judge from, I think it more probable that this difference in the tergum is due to variation and youth.
Structure of Shell and Radii.—The parietal tubes are commonly elongated in the ray of the circle: the septa are rather thick, and strongly crenated at their basal edges. The inner lamina of the walls is strongly ribbed longitudinally. The broad radii have their sutural edges formed by ridges, with numerous and closely approximate denticuli: the interspaces between the main ridges are not soon filled up, and at the bottom, each interspace usually terminates in a pore or tube; so that the radii are not solid, as in most of the foregoing species, but porose. The alæ have their edges crenated.
Basis, calcareous, of unusual thickness; the inner, or upper surface, is striated from the centre in rays, corresponding with the ribs on the inner lamina of the walls. This striated or furrowed structure in the basis, shows a tendency to its becoming tubular or porose, as may be inferred from analogous cases in [Balanus].