external. This genus of Linnaeus has at the top, and simple within. 2. Crepidda^ 
been subdivided by Lamarck into three an oval shell, with an incomplete spire, in- 
genera. i. Area, with the teeth of the dined on the edge ; the cavity separated 
hinge in a straight line, as the Area nose, into two, by a simple diaphragm. 3. Ca* 
2. Pectuncnlus, with the hinge in a curved lyptra, a conical shell, whole at the point ; 
,line ; and 3. Nucula, which deserves a dis- with a spiral diaphragm. 4. Fissurella, the 
tinct notice. shell pierced with a hole at the point. 
Nucula. This genus has been formed by 5. Emarginula, a conical shell, summit in- 
Lamarck from Area nucleus, Linn. Dau- dined, concave beneath, and the posterior 
din has also added two more species. The edge slit or grooved. 
Arks, in having their insides resplendent valve, having in its inferior face, on one 
large tooth at the hinge. The characters spiral turns on the disc of the shell. The 
are, an inequilateral, almost triangular or genus is formed by Lamarck on a fossil shell 
oblong shell ; the hinge in a broken line, be- found by Faujas among the fossils of Maes- 
set with numerous transverse and parallel tricht ; but the figuite has not yet been 
teeth ; one oblique cardinal tooth out of given. 
the line ; the beaks contiguous and turned Testacella. A univalve shell, in form of 
forwards. an oblique' cone, the summit being rather 
Unio. A transverse shell with three mus- spiral and the opening oval. This is the co- 
cular impressions ; an irregular, callous, car- vering of the posterior part of a long gaste- 
dinal tooth, stretcliing on one side, under ropodia from the isle of Teneriffe. This is 
the corselet, and articulating with one of therefore an animal between the slug and 
the opposite valve. In this genus, formed the snail. 
by Bruguiere, are placed the Mya margari- Oscana. An oval, coriaceous, almost 
tifera and Pictorum of Linnaeus. transparent univalve shell without a spire. 
Anodonta. A regular transverse bivalve The shell of this genus, and of which one 
shell, having three muscular impressions : species only is known, which is found ad- 
a simple hinge without any tooth. In this hering to prawns, is in form similar to the 
genus are placed Mytilus cygneus, anatinus. Patellae, and the animal approaches to that 
and fluviatilis of Linnaeus, with three other of the Chiton. 
species. Carinaria. A univalve shell, very thin ; 
Mytilus. A regular transverse shell with its form a cone, flattened on its sides ; its 
equal valves, shutting close, a hinge with- summit rolled, spirally and very small ^ 
out, or with one or two teeth. Lamarck the back covered with a dentated keel ; 
divides the genus Mytilus into four genera, the opening entire, oval, oblong, and eon- 
1. Mytilus, a longitudinal shell, with pointed tracted towards the angle of the keel, 
terminating beaks ; one njuscular impres- Linnaeus had placed this shell, which is ex- 
sion, and a hinge most frequently without ceedingly delicate, and as transparent as 
the posterior extremity very short ; the Patella cristata, but Dargenville, Martini, 
beaks sunk upon the short side of the shell; and Gmelin, have ranged it under the Argo- 
one muscular impression ; the hinge simple, nauts by the name of Argonauta vitrea. 
without teeth. 3. Avicula. 4. Anodonta. Bruguiere appears to have been disposed 
Pinna. The characters of this genus are, rather to have replaced it among the Pa- 
a regular bivalve shell, with equal valves, tellae ; but Lamarck has thought it right 
wedge-formed, pointed at its base, gaping to consider it as a species of a distinct 
at its superior edge; hinge without teeth, genus. 
Patella. A conical univalve shell, without disposed in a line. No change is proposed 
a spire. Linnaeus had divided these shells in this genus of Linnaeus by the French tes- 
into five sections ; the labiated, the denta- taceologists. 
ted, the mucronated, the entire, and the Sigaretus. An oval, depressed, nearly 
perforated. Lamarck has divided this ear-formed shell, with a short spiral colu- 
genus into five : t. Patella, a shell of a mella ; the opening entire, very large, 
shield pr bonnet form, without a spire, whole widened near the top of the right lip, and 
