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CHAPTER III.
Boring-shells continued—the gastrochæna, or flask-shell—origin of the name—form of the shell, and its variable shape—habits of the animal—its curious home—double mouth of the flask—the rough stone-borer, or Saxicava—origin of its name—burrows of the stone-borer—curious aspect of the rock—a sudden change—colours of the animal—the northern stone-borer—difficulty of distinguishing the species—the Petricola, or rock-shell—difficulty of procuring it—foreign and British specimens—the irus shell, or Venerupis—habitat of the animal—a caution to collectors—the gaper-shells—remarkable formation of the hinge—the blunt gaper; form of its shell—value of the gaper-shells to the student of conchology—the basket-shell, or Corbula—its general structure, and form of the hinge—the Neæra shell; its remarkable form—the siphons and their appendages.
We are still among the boring-shells, and begin with the remarkable creatures that are called by the name of Gastrochæna, because their shell gapes widely at the portion which is technically termed its belly.
At Plate I., figs. 11 and 0, may be seen two drawings of our commonest species, the Flask-shell (Gastrochæna modiolina), which, although it is extremely plentiful in certain localities, is not easy of procural. It generally lives at a depth of from twenty to sixty feet, and must be procured by the dredge or the drag, the former being preferable. The shell without the animal is by no means imposing or attractive. It is brown in colour, and small, rarely exceeding half an inch in length. A side view of the shell is seen at Plate I., fig. 9, and a back view at fig. 3 of the accompanying illustration. This latter figure is given in order to show the widely gaping form of the shell. The shape of the shell is by no
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