In the first place, as I have elsewhere written, it retracts its tube to, and even under, the level of its shell, just as a man, about to urge onwards some heavy mass with his shoulders, would depress his head to increase and concentrate his muscular power. Then follows an expansion of the neck or upper part of the ventral border, from whence the siphons protrude. This movement closes the posterior portions of the valves below the hinge, and brings their serrated points together. The next act on the part of the animal is to place its foot firmly at the base of the hole; when leaning forward, it makes a sweeping movement fully half round the cavity, pressing firmly-upon the umboes, which nature has strengthened for the purpose by two curved teeth fixed on the inside of the valves. At this stage it again reclines on its breast, and tilting up the shell as much as possible, it makes another motion round to its former position, leaning upon its back. By these intricate movements, which the Pholas appears to accomplish by a contraction almost painfully strong, it opens the rasping points of the valves. These execute a very peculiar scooping movement at the base of the cavity, and the animal having got so far, prepares itself for further exertion by a short rest. The specimen whose movements I have attempted to describe, lived in my possession for a considerable time. It bored so completely through the piece of rock in which it was embedded, that the whole of its foot dropped through the aperture, and remained in this position for months, the animal, in consequence, being unable to change its position even in the slightest degree. Each movement of this specimen, both before and while the hole at the base of the cavity was gradually being enlarged, was watched, and every striking and interesting feature that occurred noted down at the moment. Various queries were put and answered, as far as possible, by direct ocular demonstration of the labours of the animal in the vase before me. I consider myself to have been singularly fortunate in being able to view the actions of the creature from beneath, in consequence of the hole being bored through the rock. This circumstance allowed me distinctly to see what was going on at the base of the orifice. My early observations have fortunately been confirmed in other captive Pholades, which at various periods have been domesticated in my tanks.