Recently, while reading Dr. Davidson's description of his Eichwaldia Capewelli, Brit. Sil. Brach. Sup. pp. 140–1, I was much interested with that paragraph in which he states, “It had been suggested to me that the appearance of the sculpture of the surface of E. Capewelli is precisely that of certain Polyzoa one is accustomed to meet with in Palæozoic rocks, a fact that had struck Mr. R. Etheridge, jun., as well as Prof. Nicholson; but to accept the ornamentation as that of an encrusting Polyzoan we must suppose that the shell had been entirely replaced by the parasite, as sometimes occurs with Hydractinia. Sections, however, show a perfectly homogeneous structure of the whole thickness of the shell.”