CONCHOLOGY. / i 



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. Avicula heteroptera, 



A. macroptera. 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. phalaenacea. 



A. hirundo.* 



A. pallida. 



A. nebulosa. 



5. Genus Meleagrina. PI. 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. Two species, of which the 

 first is the pearl-oyster. 



Meleagrina margaritifera. Meleagrina albina. 



FAMILY XVIII. 

 Pectinea. Seven genera. 

 1. Genus Pedum. PI. IX. 

 Jlniynal. Unknown, but probably byssiferous. 



7* ' 



