MOLLUSCA. &G 
Trans.) The first important improvement in the reforma- 
tion of the genus, consisted in the separation of the pec- 
tens, which was executed by Pennant, and afterwards by 
Bruguiére and Lamark. Since new characters have been 
assigned to the genus ostrea, other separations must take 
place. It is thus defined: “ Testa bivalvis inaquivalvis, 
rudis adherens; cardine edentulo. Fossula cardinalis ma- 
joris valve etate crescens. Ligamentum semi-internum. 
Impressio muscularis unica.” The genus may be divided 
into two sections; the first having the margin of the valves 
simple, as the common oyster; and in the second the mar- 
gins are plaited, as in the O. crista-gall:. 
In consequence of this change in the generic character, 
the ostrea malleus of Linneeus, (Lister, tab. 219, f. 54.,) has 
been formed into the genus Mauxevs. ‘The shell is free, 
gapes a little at the beaks, produces a byssus, has no teeth 
in the hinge but a conical pit for the insertion of the liga- 
ment, placed obliquely on the margin of each valve. It 
was for a long time highly prized by collectors. 
The genus PEcTEN is one of the best characterised, most 
natural, and most beautiful, in the system. The shell is 
inequivalve and regular, the hinge is destitute of teeth, and 
the internal ligament is fixed to a triangular cardinal cavity. 
There are fourteen species natives of our shores. 
From the ostrea perna, ephippium, and tsogonum, Bru- 
guiére formed the genus Perna. The hinge is linear, and 
cut into a number of lengthened parallel veins, which re- 
ceive the ligament. The interstices are formed into teeth, 
which simply oppose those of the-other valve. In the an- 
terior side of the valve, near the beaks, there is a callosity, 
and an opening for the byssus of the animal. 
Lamark has constituted another genus, nearly allied to 
