226 MONOMYARIA.—OSTREAD A. 
among the most active members of this Class of 
animals; they have been called the butterflies of 
the shell-fishes, a comparison not less apt on ac- 
count of the delicacy and beautiful colouring of 
the wing-like shell, than of the agile motions which 
they exhibit. Though inhabitants of the deep 
sea, these bivalves take long and rapid leaps, 
shooting hither and thither, and fluttermg about 
through the water with an irregular zig-zag move- 
ment, produced by the alternate opening and shut- 
ting of the valves with great force. The motions 
thus performed appear to be without any determinate 
direction, and to depend upon the impact of the 
valves upon the water; but these animals (the 
Pectens at least) have the power of effecting a more 
deliberate and precise locomotion, in the perform- 
ance of which the mantle is the principal agent. 
The following observations, which I had recently 
an opportunity of making upon a young specimen 
of the Common Scallop or Quin (P. opercularis) 
which I was keeping in captivity, will serve to 
illustrate the form and office of the foot, as well as 
the faculty more immediately under consideration. 
My attention was attracted to the Pecten by 
this curious circumstance, that it was adhering by 
one valve (the flat one) to the side of the glass 
phial, at some distance from the bottom. On close 
examination with a lens, I discovered that it was 
attached by a very delicate byssus. Curious to 
ascertain how it contrived to mount from the bot- 
tom to this position, I touched it slightly, and 
caused it to loose its hold. In the course of half 
an hour I found that it had resumed the same 
position again. I again disturbed it, and began to 
watch its motions. It was lying with the convex 
