A conchological manual . it would be well to apply the term spiral disc to somuch of the shell as is seen besides the last whorl, and todescribe it as large or small in diameter, compared with thewhole : or to say that the whorls of the spire are half, or one-third, or one-fourth covered, as the case may be. Aperture of Symmetrical Ammonites Blagdeni and some others the aperture is ofan oblong square; it is then said to be sub-quadrated; in Nau-tilus triangularis it is angulated; in Ammonites Greenoughiit is of an interrupted oval shape, described as elliptical. Inth
A conchological manual . it would be well to apply the term spiral disc to somuch of the shell as is seen besides the last whorl, and todescribe it as large or small in diameter, compared with thewhole : or to say that the whorls of the spire are half, or one-third, or one-fourth covered, as the case may be. Aperture of Symmetrical Ammonites Blagdeni and some others the aperture is ofan oblong square; it is then said to be sub-quadrated; in Nau-tilus triangularis it is angulated; in Ammonites Greenoughiit is of an interrupted oval shape, described as elliptical. Inthe greater number of Orthocerata, it is rounded or entrance of the last whorl into the aperture of somerounded species of Nautilus causes it to take a semi-lunarform; if rounded at the sides it is said to be reniform orkidney-shaped: if pointed at the sides it is semi-lunar; andin some species of Ammonites, it is five-sided or quinque-lateral. c 18 * INTRODUCTION. Measurement of Symmetrical Conical ^ep/?> The width is measured across the aperture, which is thewidest part of the shell. The length (I) from the dorsal part(d) of the aperture to the dorsal part of the whorl {d) on theopposite part of the shell. The ventral part of the whorls isthat nearest to the axis, and the dorsal that which forms theoutline of the figure. NON-SYMMETRICAL UNIVALVES. These are conical, irregular, spiral, or convolute. Theconical form is when there is no enrolment of the the Patellae were described as symmetrical, there areseveral species of Patelliform shells which are not Umbrella, for instance, the apex is oblique, the shells beingplaced obliquely on the animal. In the genus Siphonaria,there is a groove on one side, where the brachia or gills of theanimal rest. In the genus Ancylus, it will be observed thatthe apex bends on one side, and the animal is like the Limnsea,which has a spiral shell. The cup and saucer Limpets, orCalyptrsedae, pr
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Keywords: ., bookcentury1800, bookdecade1840, bookidconchol, booksubjectshells
