ON ACEPHALA. 381 
will stand the test of an attentive examination. We shall 
only mention, that in some places, where limestone is scarce, 
their shells are employed with great advantage to make, by 
calcination, a most excellent lime. 
The PECTINES are so called from the form of the canali- 
culations of their shell resembling a little the arrangement of 
the teeth of acomb. They evidently differ from the oysters 
in all their anatomical relations. ‘Their habits are pretty 
similar to those of mussels, with this difference, that they are 
in general more free. They never sink in the sand, and, on 
the contrary, are always at the surface of the bottom of the 
sea, resting partly on the side, like oysters, and, as it would 
appear, at rather a small distance from the shore. The species 
which have a byssus, must, doubtless, never quit the place 
where they were born, and deposited in the egg-state ; but the 
others are said to be susceptible of a very singular species of 
locomotion, since they can raise themselves in the water, and 
even at its surface, by agitating the two valves of their shell, 
pretty nearly as birds do with their wings, and fishes with 
their fins. The small length of the ligament, its position, its 
great elasticity, and consequently the trifling separation of 
the valves, allow us to believe, that these animals can really 
move by contracting them suddenly on the fluid which they 
contain, and pushing themselves on in an opposite direction. 
But it appears by no means probable that a sort of flight can 
result from this operation. We know, indeed, but little re- 
specting the habits of the pectines. On some sea-coasts the 
larger species are eaten ; but few, except the poor, have re- 
course to this kind of food, which is hard and indigestible. 
For a long time the hollow valve of the larger species of 
pectines was used in some places by the poor asadish. It is 
capable of bearing the fire, and is sometimes adopted as a 
culinary vessel. The species of this genus are found in all 
seas, and pretty equally divided. 
