Characters and Habits of the Animal. 359 



Animal. — Mantle completely lining the shell, double at the 

 outer edge : exterior fold divided in front : interior united in 

 front, open at each end : at the posterior end forming two short 

 siphons or tubes, ciliated at the upper orifices; colour yellowish 

 white ; margin orange. 



Foot very muscular, broad, triangular, compressed, pointed, 

 orange. 



Branchice^ external, concealed between the 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 : the 

 feelers or ciliated fringe of the upper orifice («) of the mantle 

 moved slowly, as if in search of animalcuhe. Having remained 

 in this situation about ten minutes, water was ejected with con- 

 siderable force from the lower orifice, (6) which had till now re- 

 mained 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 or 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 di- 

 rected expelled them from the shell. Willi 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 propor- 

 tion to its shell, occupying when dead barely a third of the 

 space enclosed in the valves. Its mantle is slightly attached to 

 ihe shell, and to the epidermis at the margin, and appears to be 



