. A conchological manual. Shells. 18 INTRODUCTION. Measurement of Symmetrical Conical JcfrA The width is measured across the aperture, which is the widest part of the shell. The length (I) from the dorsal part (d) of the aperture to the dorsal part of the whorl (d) on the opposite part of the shell. The ventral part of the whorls is that nearest to the axis, and the dorsal that which forms the outline of the figure. NON-SYMMETRICAL UNIVALVES. These are conical, irregular, spiral, or convolute. The conical form is when there is no enrolment of the apex. Although the Patellae were de
. A conchological manual. Shells. 18 INTRODUCTION. Measurement of Symmetrical Conical JcfrA The width is measured across the aperture, which is the widest part of the shell. The length (I) from the dorsal part (d) of the aperture to the dorsal part of the whorl (d) on the opposite part of the shell. The ventral part of the whorls is that nearest to the axis, and the dorsal that which forms the outline of the figure. NON-SYMMETRICAL UNIVALVES. These are conical, irregular, spiral, or convolute. The conical form is when there is no enrolment of the apex. Although the Patellae were described as symmetrical, there are several species of Patelliform shells which are not symmetrical. In Umbrella, for instance, the apex is oblique, the shells being placed obliquely on the animal. In the genus Siphonaria, there is a groove on one side, where the brachia or gills of the animal rest. In the genus Ancylus, it will be observed that the apex bends on one side, and the animal is like the Limnaea, which has a spiral shell. The cup and saucer Limpets, or Calyptraedae, present a group which requires to be described, differently from the symmetrical or true Limpets. Their structure is very curious, and they vary considerably among. 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
