CONCHOLOGY. 
chap. nr. 
Terms em- 
ployed in 
*42?* CHAP. 
III. OF THE TERMS 
WHICH ARE 
SHELLS. 
EMPLOYED IN 
395 
Terms em- 
ployed in 
DESCRIBING 
i s 
Terms ex- 
plained. 
AS it will tend to facilitate our progrefs in the ftu- 
dy of Conchology , clearly to underftand the terms which 
are employed in defcribing (hells, and the names by 
which the different parts have been diftinguifhed by 
naturalifts, ; we (hall here give a few definitions of the 
principal terms. And that thefe definitions may be 
eafily confulted, we (hall obferve the fame order as in 
the claflification which is to be adopted. They may 
be conveniently arranged, therefore, into the three di- 
vifions of multivalves, bivalves, and univalves. 
17 
Multi- 
valves. 
I . Explanation of the Terms of Multivalve Shells. 
Multivalve (hells are compofed of more than two 
pieces. 
Articulated (teftse articulatse), when the different pieces 
of which the (hell is compofed are fiwftrongly united 
that they feem to form one (hell. 
JEquivalve fhells (teftae asquivalves), when the valves 
of the two (ides have the fame form, fixe, and por- 
tion. 
A (hell is faid to adhere (tefla adherens,) when it is 
attached to' folid bodies by fome of the pieces of 
which it is compofed : It is faid to be loofe (tefta 
libera), when it is not attached by any point. 
"Pedunculated (tefta pedunculata), when all the pieces 
of which it is compofed, are fupported by a tendi- 
nous peduncle which is fixed to folid bodies. 
Tubular (tefta tubulofa,) when the greateft part of the 
(hell is formed of a cylindrical tube. 
Safe of the fhell (bafis teftae), that part on which it 
is fupported. 
Ligament (ligamentum), is a membranous or tendi- 
nous fubftance which connects the valves together, 
and fometimes lines the cavity of the fhells. Of 
this there are feveral varieties. 
fcaly (ligamentum fquamatum), when the fur- 
face is covered with fmall granular fcales. 
» ■ prickly (ligamentum aculeatum), when the 
furface is furnifhed with fmall rough points. 
— — fmooth (ligamentum laeve), when the furface 
has neither points, fcales, nor tubercles. 
— — — punftated (ligamentum puntftatum), when the 
furface is marked with fmall cavities. 
Lid (operculum), is the name given to four fmall tri- 
angular valves articulated in the form of a crofs, 
which (hut up the fuperior orifice of fome fpecies of 
multivalve (hells. 
Peduncle (pedunculus) is the tendinous fubftance which 
fupports fome of the multivalve (hells. It is flexi- 
jble while the animal is alive, and is fmooth or 
fcaly. 
Rays (radii) j thefe are imprefiions on the external fur- 
face of fome fhells ; they are of a conical form, 
having the vertex turned towards the bafe of the 
(hell. They are only diftindlly feen in adult 
(hells. 
■■ ' filiform (radii filiformes) are long and narrow. 
fmooth (radii leves.)- 
- ■ ■ ftriated (radii tranfverfim flriati-.)=»= 
a 
Valves (vavulse) are the different pieces of which znul 
tivalve (hells are compofed. 
2. Explanation of the Terms applied to Bivalve Shells . 
A Bivalve (hell is faid to adhere (tefta adherens), Bivalve 5 , 
when it is fixed by any part of one of its valves to 
a folid body. 
It is faid to have ears (tefta aurita), when it forms 
at its bafe, one or two cotnpreffed angles. 
Gaping (tefta hians), when the valves do not (hut 
clofs. 
Bearded (tefta barbata), covered externally with an 
epidermis conrpofed of ftrong hair or bridles. 
Comprejfed (tefta compreffa), when the valves are flat, 
forming a fmall cavity. 
Heart-fhaped (tefta cordata), having the form of a 
heart •, (fubcordata) approaching to that form. 
Toothlefs (edentula) without teeth at the hinge. 
Equilateral (tefta aequilatera), w hen the anterior and 
pofterior part of the (hell is equal in form and 
figure. 
Eqmvalve (equivalvis), when the two valves are firpL 
lar in form and convexity. 
Irregular (tefta irregularis), when the form varies in 
the individuals of the fpecies. 
Lenticular (lenticularis), when the valves are round, 
and little elevated in the middle, and diminilh gra- 
dually in thicknefs towards the edges. 
Linear (tefla linearis), when the length confiderably 
exceeds the breadth, but without a cylindrical 
form. 
Tongue-fhaped (linguaeformis), flat and oblong, having 
the two extremities round and obtufe. 
Boat-fhaped (navicularis), refembling the figure of a 
boat. 
PeSlinated (pe&inata), when the valves being furnifh- 
ed with longitudinal ribs, have on their anterior fur- 
face ribs nearly tranfverfe, which form by their union 
with the fir ft acute angles. 
P.adiated (radiata), w'hen it is marked on the external 
furface with rays, ribs, or elevated ftriae, which pro- 
ceed from the extremity of the fummits, and termi- 
nate in the circumference of the valves. 
Beahed (roftrata), w'hen one of its furfaces, either an- 
terior or pofterior, being contrafted and elongated, 
terminates in form of a beak. 
Bafe (bafis). The fituation in which Linnaeus has de- 
fcribed and confidered bivalve (hells, conlifts in 
placing the beaks of the (hell turned downwurds, 
in fuch a way that the ligaments of the valves may 
be feen, fo that the bafe of the fhell is the region of 
its beaks. 
Margin of the (liell (margo teftae) fignifies the whole 
circumference of the (hell, parallel to the edge of 
the valves. It is divided into anterior, pofterior, and 
fuperior. 
— ■ anterior (margo anterior), when the (hell is 
placed on the beak of the valves, commences at 
the fide of the ligament, on the fore-part of 'the 
3 X> 2 beaks 
