SHELL. 
two teeth in one valve, and one tooth in 
the opposite valve, shutting between those 
of the other valve, as in Tellina angulata. 
Cyclas. This genus comprehends some 
shells which Linnaeus had associated with 
Tellens ; but which Bruguiere and Lamarck 
have separated from them, from their want- 
ing the fold on the anterior side. The cha- 
racters are : A suborbicular, or in a small 
degree, transverse shell, without fold on the 
anterior side j the ligament external and 
bulging ; two or three cardinal teeth, and 
elongated, lamelliform, inserted lateral teeth. 
They are fresh water shells. 
Venus. This genus of Linnmus is formed 
by shells which are regular, suborbicular, 
bivalves, provided with a crescent and a 
corslet; three cardinal teeth near toge- 
ther, and sometimes one or tw'o lateral teeth. 
The valves of this genus are generally 
pretty gibbous and thick ; constantly equal, 
and nearly of a triangular form. Lamarck 
divides this genus into two. 1. Venus, a 
suborbicular or transverse shell, with three 
approximated cardinal teeth, the lateral 
ones being more or less diverging. 2. Me- 
retrix, a transverse or orbicular shell ; witli 
three approximated cardinal teeth, and one 
isolated tooth under the crescent. The genus 
Caspa, mentioned above, is proposed by 
Bruguiere and Lamarck to comprise seve- 
ral of the Venus’s of Linnaeus. 
Ungulina. A regularly formed long bi- 
valve; the hinge formed by a very small 
^ooth between two oblique dents : the 
valves bearing the form of the finger nail. 
There is but one species in this genus. The 
binge bears some resemblance to that of 
Cardium, but the general form of the shell 
differs much from that of Cardia. 
Donax. A regular, transverse, inequi- 
lateral bivalve, with three* cardinal teeth, 
and one or two separated lateral teeth. 
Shells of this genus have much of the trian- 
gular form, their sides very unequal; they 
are solid, thick, flattened at the inferior, 
and rounded at the opposite, extremity. 
The ligament, which, in most shells with 
equal valves, is placed above the summit, 
is in these shells unequally distributed above 
and below it. Above, it is narrow and 
short ; and below, it is thick, nearly round, 
and fills the cavity of, the corslet exactly. 
Mactra. A bivalve shell, regular, trans- 
verse, inequilateral, and a little gaping, the 
cardinal tooth having a pit for the ligament ; 
lateral teeth compressed and inserted, or 
none. 
Lamarck divides this genus into three. 
1. Mactra, a transverse, inequilateral shell 
a little gaping ; the cardinal tooth folded in 
a furrow, articulating with that of tlie op- 
posite valve, and accompanying a pit for 
the ligament ; two lateral and inserted 
teeth, such is Mactra stultorum. 2. Lu- 
traria, a transverse, inequilateral shell, gap- 
ing at the extremities ; two cardinal teeth, 
oblique, and diverging, accompanying a 
large pit for the ligament ; no lateral teeth ; 
such is Mactra lutraria, Linnmus. 3. Pa- 
phia, a subtransverse, inequilateral shell, 
the valves close ; a pit for the ligament on 
the beak between or near to the teeth of 
the hinge, as in Venus divaricata. Linnaeus, 
Crassatella. A genus formed by Lamarck of 
shells unknown to Linnaeus, and which Bru- 
guiere had placed in the genus Mactra. The 
generic chararacters are an inequilateral, 
subtraiiverse shell, with close valves, with a 
sunk crescent or corslet ; the ligament in- 
ternal ; the pit for the ligament placed un- 
der the beaks, above the teeth of the h'uge. 
There are two fossil, and one recent species 
under this genus. These shells are remark- 
able for the thickness of the valves, and 
for their two deep muscular impressions. 
Trigonia. This is a genus formed by 
Lamarck, the species of which are known 
only in a fossil state. The characters of 
the genus are, an inequilateral subtrigonal 
shell, the hinge ■ formed by two large flat 
diverging teeth, transversely grooved. These 
are the Cunei of Dacosta. 
Hiatella. A genus formed by Daudin on 
two shells from Tranquebar, which appear 
to be intermediate between the genera 
Trigonia and Tridacna ; the characters are 
a transverse, irregular bivalve shell, gaping 
in its superior edge ; its hinge a tooth in 
each valve, inserted in a groove in the op- 
posite valve. 
Cucullaea. A gibbous, subtranverse ine- 
quilateral shell, with detached beaks : the 
hinge in a straight line, having a range of 
numerous teeth, transverse inserted ; and at 
the extremities two or three parallel rib-like 
teeth, the ligaments external. This genus 
is founded by Lamarck on a recent shell 
from the Indian Sea, and on a fossil shell 
from Beauvais, which Bruguiere had placed 
among the Arks ; from which these shells 
dift’er in the ribs placed at the extremities 
of the hinge. 
Area. An inequilateral bivalve shell ; the. 
hinge composed of numerous teeth, which 
lock in the interstices of those of the oppo- 
site valve, and which range in a straight, 
angular, or curved line. The ligament 
