30 CO NC H 
cockle form, but immenfely large; area, (hells formed 
like an ark; oltrea, the elcallop, common oyder, &c. 
anomia. the beaked cockle; mytilus, the mufcle ; pinna, 
the lea-wing or ham. He alio very accurately, deferibes 
the Angular habits and curious economy of many of thefe 
the) 1-fill), which lee under their re/pective names in this 
Work. 
Dr. Woodward, in his catalogue of foflils, has given a 
very good method of bivalves, on the character of the 
hinges, and alfo on the form; but his (yftem of univalves, 
is very faulty and imperfedt. The technical terms com¬ 
monly ufed for defcribiiig the parts of bivalves, and 
which are requifite for making their deferiptions intelli¬ 
gible, are as follow: The fummit, (apex,) is the part 
whereon the teeth, joints, or properly the hinges, are 
placed. The beaks, (umbones,) are the peaked ends of 
the Ihell, which molt generally hand behind the fummit, 
or that part which -anfwers to it. The margins, or bor¬ 
ders, (margines,) are the edges or contour of the Ihell, 
produced from the beak or hinge on either fide. The 
Surfaces, ([uperjicics,) concavitas & convexitas concha- 
rum ; the convex exprefies the exterior or convex fide of- 
the (hells, and the concave, the infide. The length of a 
bivalve is from the beak or hinge to the very oppolite 
extreme. The breadth is from fide to fide. The margins 
or borders are laid to be Jimilar, if equally produced or 
extended from the fummit, or of equal length ; and dijfi- 
milar, if unequal or more extended on one tide than on 
the other. The hinge, (cardo,) is the part that connects 
the two valves together, that is to fay, the joints on which 
they play in the actions of opening and (hutting. A hinge 
is faid to be inarticulate, when not fet with any viiible 
joints or teeth ; articulate , when fet with fome few; mult- 
articulate, when fet with many, or a large number. The 
furrow, (fulcus canaliculus,') is the gutter or furrow, when 
the Ihells are doled, that is extended, or runs along paral¬ 
lel to the hinge. The Hopes, (declivitas,) are the places 
which Hope or flant from the beak down the fides, and 
generally are (lightly flatted, (hallow, or concave. The 
vent, (rima,) is the opening of the Ihells on the (lopes. 
The cartilage, (cartilago,) joins the valves together at 
the furrow and at the (lopes. The flat, (planities, latus 
complanatum,) is that fide of thofe (hells that is flat; as 
the flats of the heart cockles, bears paws, &c. 
BIVALVES with UNEQUAL VALVES. 
Thefe conlift of (hells that have irregular valves, and 
/hut clofe. The fird family confifts of the pedtens, or 
efcallops. Though fome fpecies of them have equal 
Valves, yet, as the far greater number have unequal 
valves, viz. a flat and a concave tide, they are ranged un¬ 
der this general head. The fame particular likewife occurs 
in the families of the fpondyles and oyders. 
ESCALLOP.—The eflential character of the efcallop 
family'', is a trigonal finus, and an elallic cartilage tor its 
hinge in the very center of the top ot the (hell. The fub- 
ordinate charaders of efcallops are their being eared ; in¬ 
deed mod authors have injudicioufly made it the chief 
charader, whereas there are other eared fhells belides 
efcallops, as the fpondyles, margaritiferas, &c. and, vice 
<verfa, there may be efcallops without ears. The other 
fubordinate charader is to have the top run into a per- 
fed (trait line, and thence gradually widen to a round 
bottom. The fpecies are numerous, fome whereof are 
v/ery curious, and of great beauty, as the ducal mantle, 
the compafs or foie, the duck’s foot or coral-efcallop, &c. 
It is worthy of remark, that the colours of the under 
fhells of efcallops are always fainter than the colours of 
the upper /hells, and fometimes the valves are differently 
coloured, as the compafs or foie, which has one valve of 
a cheinut brown, the other valve milk white. Mod au¬ 
thors rank thefe fhells as a particular family, and call 
them pedens. Gualteri makes diderent genera of thofe 
wit!) equal, and thofe with unequal, valves; the former 
he calls peden, the latter concha pedinata; and the efcai- 
O L O G Y. 
lops with unequal or (ingle ears, he calls pedunculi. Lin- 
nseus makes them a genus of oyders, and has accordingly 
arranged them under the generic name Ostrea. It is 
faid, that efcallops will move fo ftrongly. as fometimes 
to leap out of the bafket wherein they are placed when, 
taken: their mode ot leaping, or railing themfelves up, 
is by .forcing their under valve againft the .body whereon 
they lie. 
The chief kinds of foflil efcallops yet in an undifeo- 
vered date, are as follow.: The firlt is about the fize of 
the common oyder, with large but unequal ears, of a 
perfedly round contour; the furface tranfyerfely thick 
fet with prominent (harp thin ridges, like plates. The 
valves are equal. Thefe are found very frequently in the 
quarries at Thame in Oxfordfbire. A fecond kind, very 
elegant, is about double the fize of a cockle, the valves 
unequal, one being quite flat, the other exceedingly con¬ 
cave. It is thickly ridged lengthways, with many com¬ 
mon ridges and intermediate ones, that are very promi¬ 
nent or high, and the furrows are broad and deep. It is 
found in the quarries of Dorletfliire, Wiltlhire, and the 
adjacent counties; and fometimes in-the clialk-pits of 
Kent and Surrey. 
SPONDYLE.—The fecond family in this divifion is 
the fpondyli. The fpondyles are mod, generally eared 
(hells with unequal valves, rude or uncouth in diape, par¬ 
taking of the ruggednefs of the oyder, with i’omewhat of 
the efcallop form, fo as tp produce a medium between 
the two families. However, the fpondyles, like.the efcal¬ 
lops, have Com6 fpecies with equal valves, and without 
ears. The eflential character is the hinge, which in the 
tipper fheil coiifids of a triangular hollow and cartilage, 
like the efcallop, in the very center; on each fide of 
which is a large deep cavity, and a very large thick and 
prominent tooth or joint lies on each fide of the cavity. 
The fummit and beak of the under valve is alio extremely 
thick and Arong, and extends from the hinge outwards 
into a broad triangular (lope or flat. 
Some kinds of fpondyles are thickly and curioufly fet 
with long thorns or fpikes ; thefe are generally called 
thorny oyjlers, and, when perfect, are greatly valued, This 
family is not very numerous in its fpecies. Lider, Wood¬ 
ward, Gualtieri, Linnaeus, and Meufchen, all rank them 
as a particular genus, by the name of fpondylus; but 
Rumphius, Argenville, and Davila, rank them very er- 
roneoudy as oylters. 
OYSTER.—The third family in this divifion is the of- 
treum, or oyder. The oyders have unequal valves, though 
there are fome fpecies that have equal valves, but none are 
eared. The hinge of this family has not any teeth, but 
confids of one large inarticulate gutter running the length 
of the top of the Ihell, in both fhells alike, and is covered 
and filled wit£i a ftrong cartilage. The fpecies are very 
numerous; fome of which are curious, though not beau¬ 
tiful, and bear a large price, as the hammer oyder, the 
cockfcombs, &c. This family is ranked as a d i It in 6t one 
by all authors, but with many additions or omifiions : as 
for example, Linnaeus ranks the efcallops with them, and 
Argenvilie and others the fpondyles,’ while Lifter ranks 
the hammer oyder, and fome others, as efcallops. 
It is not uncommon to fee on oyder-(hells, when in a 
dark place, a filming matter or biuifli light like phoi’pho- 
rus, which (ticks to the fingers when touched, and conti¬ 
nues fhining and giving light for a conliderable time, 
though without any feniible heat. This fhining matter 
being fubjedted to the mierpfeope, is found to confiit of 
three kinds of animalcules; the fird whitifh, and having 
twenty-four or twenty-five legs on a fide, forked, and a 
black (peck on the head, the back like an eel with its (kin 
(tripped off. The fecond fort is red, refembling the Com¬ 
mon glow-worm, with folds on its back, and legs like 
the former, a note like a dog, and one eye in front of 
the head. The third kind is lpeckled, with a head like a 
lole, with many tufts of whitifh hairs on the fide.s of it. 
The fofiil oyders yet undifeovered in a recent or living 
(fate, 
