15. [BALANUS] SPONGICOLA. Pl. [4], fig. [1 a]-[1 d].
BALANUS SPONGICOLA. Brown’s Illustrations of the Conchology of Great Britain (1827), pl. 7, fig. 6: 2d edit. (1844), pl. 53, figs. 14-16.
Parietes generally smooth, sometimes longitudinally folded; coloured pink: orifice toothed. Scutum longitudinally striated. Tergum, with the apex produced, without a longitudinal furrow; spur truncated, about one third of width of valve.
Var. with the walls slightly folded longitudinally.
Hab.—South coast of England, and Tenby in South Wales, often imbedded in sponges; attached also to shells and rocks in deep water; Mus. Brit., Jeffreys. Algiers, on Mytili and Serpulæ, with [B. perforatus], Mus. Mac Andrew. Madeira, with [B. tulipiformis], Mus. Lowe. Lagulhas Bank, Cape of Good Hope, on detached kelp, with [B. Capensis], Mus. Sir J. Ross. Imbedded in sponge with [Acasta spongites], Mus. Bowerbank. Var. West Indies.
Fossil in Coralline Crag, Mus. S. Wood.
General Description.—Shell tubulo-conical; orifice of moderate size, rather deeply toothed; colour dull pink, or purplish, or dark flesh-colour; sometimes the radii are paler, sometimes of the same colour with the parietes. Surface smooth when well preserved, having transverse rows of minute spines. In the West Indian variety the walls are slightly or much folded, but I will describe this form separately. Size of largest specimen (Mus. Jeffreys), .6 of an inch in basal diameter.
Scutum, with fine ridges radiating from the apex, and with the lines of growth, crenated: internally, the articular ridge is small, adductor ridge short and barely distinct: there is a rather deep and narrow pit for the lateral depressor muscle. The whole valve is much thinner than in [B. trigonus], which in most respects it closely resembles. Tergum, with the apex pinkish purple, produced or beaked, but the beak is not needle-like, as in [B. psittacus] and its allies, for the carinal margin is perfectly preserved up to the tip. Externally the valve is nearly flat, for the longitudinal furrow is very shallow. The spur is about one third of the width of the valve; its lower end is abruptly truncated: in European specimens ([1 b]) the whole basal margin, on the carinal side, slopes down to the spur in a straight line, which, together with the sharpness and production of the basi-scutal angle of the spur itself, gives to the whole valve a peculiar appearance: in the specimen ([1 c]) from the Lagulhas Bank, the basal margin on the carinal side is a little more hollowed out, but it is quite impossible to doubt about the specific identity of these specimens: in the West Indian variety ([1 d]) the basal margin on the carinal side forms a distinct but obtuse angle with the spur. In all cases the crests for the depressor muscles are very feebly developed.