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T H E F O S S I L B A L A N I D A E compartments are a little arched in, tending to make the shell somewhat globular. The true basis is extremely narrow (fig. 5d): it is deeply grooved, from clasping the thin, cylindrical stem of the coral to which it has adhered; and I have seen specimens in which the opposite edges o f the groove had met, a tube having been thus actually formed. From the grooved basis, and from the elongation of the shell in the rostro-carinal axis, this variety presents so close a general resemblance to Balanus calceolus, and its allies, that I have seen it in a collection arranged on the same tablet with / a fossil specimen of B. calceolus. Notwithstanding the above several strongly marked characters, by which this variety differs from the ordinary form, there is a resemblance in colour and aspect, which, though difficult to be described, made me from the first suspect that the two were specifically identical. In no point o f real structure is there any difference, excepting that, perhaps, the pores in the basis are here rather smaller; but this might arise from the little development of the peculiar basis. Having come to this conclusion, I was interested by finding a specimen (fig. 5e) in Mr Wood’s collection, which had originally fixed itself (judging from the form of the basis) on a thick cylindrical stem, but which had subsequently grown on to an adjoining flat surface; consequently, one side of the shell presented all the peculiar characters of the present variety, but not strongly pronounced, whereas the other side, at the rostral end, was undistinguishable from the ordinary form. The unequal development of the rostrum on the two sides was very striking, and clearly showed how great an effect could be produced by the nature of the surface o f attachment.