ORDER TESTACEA. 97 
to the other. The animal (EcHt1on, Pol) has a small vestige 
of a foot, similar to that of a pecten, which slips between the 
emargination and the plate that closes it, and perhaps serves 
to direct water to the mouth, which is close to it. 
These shells are found attached to various bodies, like the 
ostreee. They occur in every sea. 
PLACUNA, Brugq., 
A small genus, allied to the anomiz, in which the valves are 
thin, unequal, and frequently irregular, as in the latter, but both 
entire. Two projecting ribs, like a chevron, are seen in the 
inside of one of them, near the hinge. 
The animal is not known, but it most resembles that of the 
ostreze, or that of the anomie. 
SPONDYLUS, Lin., 
A rough and foliaceous shell, as in the ostrez, and frequently 
spiny, but the hinge is more complex ; besides the cavity for 
the ligament, analogous to that of the ostrez, there are two 
teeth to each valve, that enter into fosse in the opposite one. 
The two middle teeth belong to the most convex valve, which 
js usually the left one, and which has a projecting heel flat- 
tened as if sawed through behind the hinge. The animal, 
like that of a pecten, has the borders of its mantle furnished 
with two rows of tentacula, some of the external ones being 
terminated by coloured tubercles; before the abdomen is a 
vestige of a foot formed like a broad radiated disk, on a short 
pedicle, and endowed with the faculty of contraction and ex- 
pansion. From its centre hangs a filament terminated by an 
oval mass, the use of which is unknown. 
The spondyli are eaten like oysters; their shells are fre- 
quently tinged with the most brilliant colours; they adhere 
to all sorts of bodies. 
VOL. XII. H 
