44. [BALANUS] VARIANS. Pl. [8], fig. [9].
B. VARIANS. G. B. Sowerby, in Darwin’s Geolog. Observ. on South America, (Sept. 1846), Tab. 2, fig. 4, 5, 6.
Parietes moderately thick: radii with their upper margins very oblique; sutural edges almost smooth, or finely crenated: basis finely porose. Tergum with the spur small, narrow, bluntly pointed.
Hab.—Port St. Julians, Patagonia; ancient Tertiary formation. Eastern plain of Tierra del Fuego (?).
This species comes so close to [B. unguiformis], that I have some doubt whether they ought to be specifically separated: the whole shell is stronger, and the basis can be seen to be porose when a polished section is made: the spur of the tergum is smaller, more pointed and more medial, but these latter differences may be due to mere variation. Should [B. varians] and [unguiformis] prove to be the same species, the latter name has the priority.
General Appearance.—Shell moderately strong and thick; shape conical or tubular, or even inverted conical; orifice moderately toothed, large, sub-trigonal; walls either smooth or longitudinally folded; the elongated specimens are most apt to be smooth. The Radii are narrow and oblique. Diameter of largest specimen above three-quarters of an inch.
Scuta, with the lines of growth moderately prominent; the internal surface of the valve has been ill preserved; but a very prominent, hardly reflexed, articular ridge, can be distinguished, as well as the absence of an adductor ridge. Terga, with no distinct longitudinal furrow running down the valve: spur short, bluntly pointed, narrow, about one fifth or one sixth of width of valve; placed at above its own with from the basi-scutal angle; the basal margin, on each side close to the spur, curves towards it. Internally, all that can be distinguished, is that the articular ridge is prominent.
Parietes; their inner surfaces appear to have been nearly smooth; the absence of parietal pores could be made out only by polishing a transverse section. The Radii are narrow, and have their upper margins very oblique and rather smooth: in the elongated varieties the sutural edge appears to be almost absolutely smooth; in the conical specimens it is slightly crenated, the septa being apparently not denticulated. In living species we have a similar variation in the state of the sutural edges of the radii, in [B. balanoides] and [crenatus] the edges being much smoother in much elongated specimens than in other varieties. The alæ have their upper margins less oblique than those of the radii, with their sutural edges barely crenated. The basis is either flat, or, in the elongated specimens, deeply cup-formed; in section it can be seen to be finely and irregularly porose.