336 Our Food Mollusks 



and in young individuals is often variously and beauti- 

 fully colored. This form is much the most common in 

 the market. The northern scallop when full grown pos- 

 sesses a shell about seven inches in diameter, that is with- 

 out radiating grooves or pigment. It is now so difficult 

 to find that it is seen in few markets outside the state 

 of Maine. 



Pecten irradians inhabits shallow waters near the shore 

 line, and is usually found where eel-grass is abundant. 

 The reason for this will presently appear. Like the other 

 members of the genus, it is in many respects a very 

 highly specialized form among bivalves. Along its 

 mantle edge, for example, are many complex eyes that 

 are visual organs of surprising acuteness. The creature 

 has the habit of lying, at times, on the surface of matted 

 eel-grass, and on being approached, becomes alarmed, 

 flaps itself off of its support, and sinks to the bottom. 

 Like a few other bivalves, the adults are able to swim, but 

 in a very peculiar manner. 



Lying on the bottom, they sometimes may be observed 

 to snap the valves of the shell together, and water being 

 thus ejected from the mantle chamber, the body is forced 

 in the opposite direction. It might be assumed from the 

 examination of an individual held in the hand that the 

 animal must move in swimming with the hinge edge of 

 the shell forward, but quite the reverse usually is true. 

 It may be puzzling to understand why the expelled water 

 should not all escape from the edges of the shell opposite 

 the hinge where the gape is widest ; but when the mantle 

 folds are examined, a very wide and thick flap is found 

 on the edge of each, which, when the water in the cham- 

 ber is put under pressure by the closing of the shell, is 

 thrown inward in such a manner as to prevent its escape 



