BALANUS MONTAGUI. Brown’s Illustrations of Conchology (2d edit. 1844), Pl. 53, fig. 24-26.
[103] As the plate to the Supplement to the ‘Encyclop. Brit.’ is marked as engraved in 1817, I presume Dr. Leach gave a proof to Lamarck, thus enabling him to publish this species four years before the Supplement itself appeared.
Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed feebly: scutum with the articular ridge abruptly cut off at its lower end: tergum with the spur rounded-truncated, about one third of width of valve.
Hab.—South coast of England; South Wales, (Tenby); Portugal; Naples; Sicily; Cape of Good Hope.
This species and the three following, have caused me much doubt and trouble. At first I took the view here adopted, namely, that they were distinct: more careful examination made me run them altogether under one name. Finally, after still further deliberation, and the examination of a few additional specimens, I concluded there was the least chance of error in classing them separately. I may here mention, that in some sponge from the Cape of Good Hope, this species was mingled with [Balanus spongicola].
General Appearance.—The shape is usually that of a cup, the orifice being, in most cases, rather large, and deeply notched, owing to the great obliquity of the radii and alæ. The surface is generally smooth, but furnished with sharp calcareous projections. The colour is pinkish, and chiefly in the upper part of the shell; the lower part is often yellowish from the preserved epidermis. The parietes in the carino-lateral compartments are always narrow, being only one sixth or one seventh of the width of the parietes in the lateral compartments. The radii are not very wide, never equalling in width the parietes. The basis is moderately deep, and sometimes very deep, being even occasionally curled like a horn on one side. The specimens from Lisbon and Naples are a little larger than any British specimen which I have seen; the former being .3 of an inch in basal diameter.
Scuta: these are striated longitudinally in close lines, generally plainly, but to a variable degree. The whole valve is flat, thin, and rather elongated, with barely a trace of an adductor ridge: the articular ridge is short and rather prominent: it terminates downwards abruptly, and this does not appear to be the case in the two following species. Terga: these are small compared with the scuta, they are slightly beaked: the spur is truncated but rounded, more especially on the carinal side; it is rather more than one third of the width of the whole valve. The articular ridge and crests for the depressor muscles are feebly developed.
Structure of the Parietes and Radii.—The state of the inner surface of the parietes varies much; generally they are slightly ribbed close to the basis, the ribs sometimes extending up to the sheath; rarely the surface is quite smooth. The edges of the radii are slightly crenated. The upper internal surfaces of the radii, where overlying the alæ, are usually marked by feeble undulating lines, nearly parallel to the basis. The alæ have very oblique summits.
Basis: this is generally of a regular cup-like form, and about two thirds as deep as the shell is high; sometimes it is pointed at the bottom and distorted. The edge is feebly crenated, and rarely quite smooth. It is often penetrated by small rounded irregular holes; and I have seen specimens from the Cape of Good Hope with parts like a sieve.