HEART-SHELLS. 275 
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 animalcule. . Having re- 
mained 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 exami- 
nation, 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 
