Page:Natural History, Mollusca.djvu/307

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295
STONE BORERS.

the siphons when they are extended. Such an one is now before me, which has been in my possession

Natural History - Mollusca - Gastrochaena.png

GASTROCHÆNA.

in a living state for several months, during which time it has slightly increased the length of its projecting tube by the addition of shelly matter. Internally the tube gives indications of a division into two, but the partition does not extend to the middle from either side. The crimson tips of the siphons may often be seen when the animal is undisturbed, just reaching to the tip of the tube, or projecting in the smallest degree beyond it. The investing tube is found, on carefully breaking the stone, to enclose the animal with its valves in a sort of flask or bottle. This species (G. modiolina) is reckoned among our rarer shells.


Genus Saxicava.

No accessory tube is formed by the animals of this genus, which live in the hardest rocks, especially those of calcareous formation. The shell is oblong and gaping, with prominent beaks; the