SHELL. 
Miination of which led to this separation, is 
the Hercules club, considered by Gmelin as 
a Teredo, and named by him Teredo 
clava. The shells of this genus seem to 
differ from the Teredines only in con taining 
one, whilst the Teredo contains two pair of 
valves. The Pholas hians and Pholas 
teredula of Gmelin appear to be. merely 
the interior valves of two species of Fis- 
tulancE. 
From the several species which Linnaeus 
has collected under his genus Anomia, La- 
marck and Bruguiere have formed six dis- 
tinct genera, which they have named Ano- 
mia, Calceola, Terehratnla, Crania, Pla- 
cuna, and Hyalaea, which they describe as 
being thus characterised : 
Anomia, an irregular shell, formed of 
two unequal valves, the inferior of which is 
either pierced or grooved at its beak, the 
opening being closed by a small opercu- 
lum, or third valve, which fixes on other 
bodies, and is attached by a ligament. 
The hinge is without teeth. If is by pos- 
sessing this tliird body, therefore, whether 
considered as valve or operculum, that this 
genus is distinguished. 
BIVALVE SHELLS. 
Calceola. A regular bivalve shell, with 
unequal valves, the largest being in the 
form of a half sandal, and the smallest flat, 
semiorbicular, and resembling an opercu- 
lum; the hingq with from one to three 
small teeth. This shell is only known as a 
fossil, and is considered by Gmelin as an 
Anomia (Anomia sandalium). It is very 
thick, and about an inch in length. Its 
back is flattened ; its interior is striated 
longitudinally, and its valve or operculum, 
concentrically. 
Terebratula, a regular bivalve shell, with 
unequal valves, fixing itself by a ligament 
or short tube ; the largest valve perforated 
at its summit, which is prominent and re- 
curved; hinge with two teeth. The regu- 
larity of the valves, the absence of any 
operculum, the position of the hole, and 
the form of the hinge, separate this genus 
from that of Anomia. 
Crania, a regular bivalve shell, withun- 
e((ual valves, the inferior almost smooth, 
and nearly round, and pierced in its inter- 
nal face with three unequal and oblique 
holes ; the superior valve very convex, fur- 
nished internally with two projecting cal- 
losities. The three holes in the inferior 
valve of this shell, induced Lamarck and 
Bruguiere to separate it from the Anomiae, 
and place it in a distinct genus. The spe- 
cies described by Lkinseus is named by him 
Anomia craniolaris. 
Placuua, an irregular bivalve flat shell ; 
the interior hinge composed of two diverg- 
ing ridges, which serve for the attachment 
of a ligament. Linnaeus has arranged two 
species, Anomia placenta, and Anomia sella, 
under the genus Anomia. 
Hyalaea, a regular bivalve shell, with 
unequal, bulging, Connies, transparent 
valves, gaping under the beak, and tricus- 
pidated at the base. This genus is formed 
by Lamarck, from a shell described by For- 
skal, and denominated in Gmelin’s Linnmus 
Anomia tridentata, caudata ^and retusa. 
The Clio pyramidata of Linnmus are also 
referable to this genus. 
Lingula, a long flat shell, formed of two 
valves, nearly equal, truncated in the fore- 
part; the hinge without teeth; the beak of 
the valves pointed, and joined to a tendi- 
nous tube, which as a ligament to the shell, 
and fixes it to other solid bodies. Linnaeus, 
who knew only of one valve of this shell, 
termed it Pdtilla unguis. 
Corbula is an unequal-valved, sub-trans- 
verse, smooth, regular shell ; with a coni- 
cal cardinal tooth, curved, or turned up- 
wards, on each valve; interior ligament, 
and two muscular impressions. This genus 
is characterised by the inequality of its 
valves, one of them being nearly a third 
larger than the other. These shells are 
found fossil at Grignon, near to Versailles. 
Orbicula is a genus formed by Lamarck 
from a shell which was discovered by Mul- 
ler, and which was named by him Patella 
anomala. Its differing so entirely from 
Patellae in being a bivalve, ‘and its being in- 
habited by an animal totally different from 
that of the Patella, has induced Lamarck 
thus to separate it from the genus Patella. 
This shell is orbicular, but rather flattened, 
and composed of two valves ; by the lowest 
of which, which is extremely delicate, it 
adheres to other bodies. Its hinge is not 
known. 
Pandora is a regular inequivalved, and 
inequilateral shell ; with two cardinal, ob- 
long, unequal, and diverging teeth, in the 
upper valve ; and two oblong pits in the 
other valve ; and interior ligament, and two 
muscular impressions. The shell which gives 
rise to this genus is Tellina inmquivalvis, of 
Linnseus ; the inequality of the valves be- 
ing the circumstance which is supposed to 
warrant the separation. This shell is named 
Pandora margaritacea, by Bruguiere. 
