mantle and the body. Body soft, completely included within the valves. On being placed in a vessel of sea-water, the valves of the shell gradually opened to the extent represented in the drawing [about one-fourth of an inch]; the feelers or ciliated fringe of the upper orifice of the mantle moved slowly, as if in search of animalculæ. Having remained in this situation about ten minutes, "water was ejected with considerable force from the lower orifice, which till now had remained motionless. The expulsion of the water appeared to be effected by a sudden contraction of the muscles, because this was never done without the valves nearly closing at the same instant. After a few seconds the valves gradually returned to their open position, and remained quiescent as before, till the water was again ejected with a jerk; this alternating process was repeated at unequal intervals during the whole time my specimens were under examination, but at shorter intervals on receiving fresh supplies of sea-water, when I suppose food (its quality I could not ascertain) was more abundant.
"The animal appears to be insensible both to sound and light, as the presence and absence of either did not at all interrupt its movements; but its sense of feeling appeared to be very delicate: minute substances being dropped into the orifice of the mantle instantly excited the animal, and a column of water strongly directed expelled them from the shell. With so much strength was the water in some instances ejected, that it rose above the surface of three inches of superincumbent fluid. Animal small in proportion to its shell, occupying when dead barely a third of the space enclosed in the valves. Its mantle is slightly attached to the
