. A conchological manual. Shells. Fig. 60, Melo, obliquely -plaited; 61, Turbinellus, horizon- tally plaited; 62, Ancillaria, varicose, tortuous; 63, Na- tica, straight. OPERCULUM. The aperture of many species of shells remains constantly open ; but in a great number of species it is occasionally closed, whenever the animal is retracted within the shell, by a calca- reous or horny piece called the operculum. This must be dis- tinguished in the first instance from another kind of calcareous covering, which in some univalve shells serves to close the aper- ture during a certain portion of the ye
. A conchological manual. Shells. Fig. 60, Melo, obliquely -plaited; 61, Turbinellus, horizon- tally plaited; 62, Ancillaria, varicose, tortuous; 63, Na- tica, straight. OPERCULUM. The aperture of many species of shells remains constantly open ; but in a great number of species it is occasionally closed, whenever the animal is retracted within the shell, by a calca- reous or horny piece called the operculum. This must be dis- tinguished in the first instance from another kind of calcareous covering, which in some univalve shells serves to close the aper- ture during a certain portion of the year. This piece, named the epiphragm, although hardened and shelly in appearance, is no real part of the animal or of the shell ; being only a secretion temporarily hardened, for the purpose of defending the animal from external influences during the hibernating or torpid season, to be dissolved when that season is at an end. On examining this piece, it will be observed that it is not formed. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sowerby, G. B. (George Brettingham), 1812-1884. London : Henry G. Bohn
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectshells, bookyear1842
