A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . {Oioen, Gra)it,) Adult characters. The attain-ment of the full-growth proper toeach species is usually marked bychanges in the shell. Some bivalves, like fhe oyster,and gryphcea (fig. 26), continue toincrease in thickness long afterthey have ceased to grow outwards; ^^- ^^ ^^ ofgryj^hoea*the greatest addition is made to the lower valve, especially nearthe umbo; and in the spondylus some parts of the mantle secretemore than others, so that cavities, filled with fluid, are left in thesubstance of the shell. The ad
A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . {Oioen, Gra)it,) Adult characters. The attain-ment of the full-growth proper toeach species is usually marked bychanges in the shell. Some bivalves, like fhe oyster,and gryphcea (fig. 26), continue toincrease in thickness long afterthey have ceased to grow outwards; ^^- ^^ ^^ ofgryj^hoea*the greatest addition is made to the lower valve, especially nearthe umbo; and in the spondylus some parts of the mantle secretemore than others, so that cavities, filled with fluid, are left in thesubstance of the shell. The adult teredo 2Ci\A. fistulana close the end of their burrows ;the pholadidea fills up the great pedal opening of its valves; andthe aspergillum forms the porous disk from which it takes itsname. Sculptured shells, particularly ammonites, and species ofrostellaria andfusus, often become plain in the last part of their * Fig. 26. Section oigryphofa incurva, Sl)y. Lias, Dorset, (original; dimi-nished one half), the upper valve is not much thickened; the interior is filledwith 44 MANUAL OF THE MOLLUSCA.
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License: Licensed
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmollusks, bookyear185
