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Show 146 MR. T. D. A. COCKERELL ON CLAUSILIA RUGOSA. [Feb. 17, shell, which remains uninjured. Instead of merely repairing the wall of the shell, the animal has constructed a new aperture, which, although not so perfectly formed as the first one, still has the lamellae and general structure of the normal mouth. A similar monstrosity is figured by Moquin-Tandon, Hist. Nat. Moll. France, pi. xxiv. fig. 19. The other two specimens (fig. 3) are noticeable because, although from the same place, they differ so much in size, form of the aperture, Specimens of Clausilia rugosa from Isleworth, Middlesex. Figs. 1, 2. Specimen with two apertures, the new one having been formed after a fracture of part of the body-whorl. Fig. 3. Specimens having different characters, A being fully developed, and B probably stunted by an algoid growth.-A. Nearly symmetrically pyriform aperture of clean specimen, 12 millim. long; B. Nonsymmetrical^ pyriform aperture of specimen coated with alga, and 10 millim. long. and geneial structure that they look almost like examples of different species. It will be noticed that the larger specimen, 12 millim. long:, with the nearly symmetrically pyriform aperture, is clean ; while the smaller one, 10 millim. long, with the asymmetrically pyriform aperture, is coated with an algoid growth, which was green and conspicuous when the shell was found. Possibly this affords us a clue to the reason of the differences between the shells. Messrs. Bornet and Flahault (Bull. Soc. Bot. France, 1890) have been investigating certain parasitic algse which live in shells, and, penetrating under the epidermis, destroy the hard structures by degrees. This has been observed in marine and freshwater shells, and is very possibly one |
