96 CLASS ACEPHALA. 
valve in particular. A depression is observed at the hinge for 
the ligament. 
PLAGIOSTOMA, Sowerb. 
The oblique shell of a lima, flattened on one side; very 
small ears; the valves more convex, striated, without scales ; 
the opening for the byssus smaller. ound in formations an- 
terior to chalk. 
PACHYTES, Defr. 
Nearly the same form as the pectines: shell regular, with 
small ears; a flattened transverse space between their sum- 
mits, which in one of the valves is marked by a triangular 
notch, in which passed the ligament. Found in chalk. In 
the : 
DIANCHORA, Sowerb., 
The valves are oblique and irregular ; one of them adherent, 
and with a perforated summit, the other free, and with ears. 
Popopsis, Zam. 
Regularly striated valves, without opercula; the summit of 
one of them more salient, truncated, and adherent, frequently 
very thick, and forming a sort of pedestal to the shell. 
Although multivalve, we should approximate the 
ANOMIA, Brug., 
To the ostree. The anomie have two thin, unequal, irregu- 
lar valves, the flattest of which is deeply notched on the side 
of the ligament, which is similar to that of the ostree. The 
greater part of the central muscle traverses this opening, to be 
inserted into a third plate, that is sometimes stony and some- 
times horny, by which the animal adheres to foreign bodies, 
and the remainder of it (the muscle) serves to join one valve 
