An example of one of these irregular tubes is shown in fig. 1, in which is represented a specimen in Mr. Sowerby’s collection. The animal has in this instance taken a fancy to a large piece of shelly and thus succeeded in disguising itself very effectually. Sometimes, when it settles down in a spot where oyster-shells have been thrown, it will bore completely through them, and attach itself to them in such a manner that the oyster-shell forms a kind of collar round the flask.
If the reader will now refer to Plate I., fig. 11, he will see why the tube is double. It is made for the reception of the double siphon, the two portions of which are united throughout their length, and have the extremities close to each other. They are not permanently extended, but are capable of being withdrawn almost wholly into the shell, a movement which generally takes place when the animal is alarmed. The shell is extremely frail, so that to take it out of its tube unharmed is not always easy. It is a very common species in the Mediterranean, as well as in the British localities which it chooses. It is, however, extremely local, and chiefly affects the southern coasts, especially those off Devonshire.
Close to the Flask-shell, and rather above it, is delineated another boring-shell, which is appropriately called the Rough Stone-borer (Saxicava rugosa), because it excavates rocks, and the shell is covered with wrinkles.
In this animal the siphons are comparatively short, and the general shape of the shell is not unlike that of the last-mentioned species. The Saxicava mostly attacks limestone, though it does not bore to a very great depth, its tunnel rarely exceeding six inches in depth. It is so plentiful in some localities, that the whole face of the rock is completely honeycombed by its numerous burrows; and considering the hardness of the stone and the delicacy of the shell, the fact of its ability to pierce so stubborn a substance is really
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