13 
GERVILLIA, Defiance. 
Gen. Char. An unequal-valved, unequal-sided bi- 
valve,, oblique, much elongated ; beaks near 
the anterior extremity ; hinge long ; divided 
into several pits„ and furnished with many, more 
or less lam ell i form, teeth ; one muscular im- 
pression in each valve. 
A genus nearly related to Perna. The species upon 
which it is founded has nearly parallel edges ; but seve- 
ral others that possess the same characters in the hinge, 
are ovate, and more or less taper towards the extremi- 
ties. The hinge consists in a long transverse area, con- 
taining 3 or more shallow hollows destined to receive 
the ligament ; about the inner edge of this area are a 
number of irregular interlocking lamellar teeth, varying 
in their direction and size in different parts of the same 
hinge and in different species ; those placed towards the 
anterior extremity are, in the type of the genus, small 
and longitudinal ; the others long and transverse : in other 
species they are all either oblique or transverse. The 
casts of the typical species indicate a shell that gapes at 
one if not at both extremities ; the other species are close. 
The shell in all is thick, and probably consists chiefly of 
pearl. 
Mons. Defrance established this genus in the Diction - 
naire des Sciences Naturelles , from casts discovered by 
Mons. de Gerville,— -in commemoration of whom he has 
named it, and thus done honour to a Naturalist whose zeal 
and urbanity justly merit it. — Other species have been 
added to it by Mons. Eudes-Deslonchamps, in conse- 
quence of the resemblance in their hinges. Hereafter 
these will form at least a sub-genus. 
