CONCHOLOGY. Tt 
small, canaliculated ; a byssus; mouth surrounded with fringed 
lips, besides two pair of labial appendages, a large contractile 
muscle, nearly posterior. 
Shell. Foliaceous or not; always nacred, subequivalve, of a 
subregular form, but somewhat variable ; valves oblique, the left 
one with a little notch, through which the byssus passes; hinge 
linear, toothless, or with two small rudimentary teeth; ligament 
more or less exterior, placed in a narrow groove; one very large 
posterior muscular impression and one very small anterior. In- 
habits the British and American coasts. Nineteen species. 
Avicula nudata. 
A. macroptera. 
Avicula heteroptera. 
A. crocea. 
A. semi-sagitta. A. Atlantica. 
A. falcata. A. papilionacea. 
A. Tarentina. A. physoides. 
A. squamulosa. A. virens. 
A. Costellata. A. trigonata. 
A, lotaria. A. phalenacea. 
A. hirundo.* A. pallida.* 
A. nebulosa.* 
5. Genus Meleagrina. Pl. IX. 
Animal. As above. : 
Shell. Subequivalve, rounded, squamous, a sinus posteriorly 
for the passage of the byssus, at which place the left valve is 
notched and narrow; hinge linear and destitute of teeth; liga- 
ment marginal, elongated, partly exterior, and dilated in the 
centre. Inhabits the Indian Ocean. ‘T'wo species, of which the 
first is the pearl-oyster. 
Meleagrina margaritifera. Meleagrina albina. 
FAMILY XVIII. 
PecTines. Seven genera. 
1. Genus Pedum. PI. IX. 
Animal. Unknown, but probably byssiferous. 
7T* 
