Lamarck's Genera of Shells. 37 



Type. Avicula crocea* . 

 Shell smooth, muddy yellow, not spotted ; wing obliquely 

 divaricate. 



Isle of France. 15 Species. PI. I. Fig. 84. 



5. Meleagrina t- 



Shell equivalve, quadrate -rotundate, externally squamose ; 

 lower cardinal margin straight, anteriorly not caudate. A sinus 

 at the posterior base of the valves, for the passage of the byssus ; 

 margin of the left valve at that part narrow, emarginate. Hinge 

 linear, without teeth. Facet of the ligament marginal, elon- 

 gated, subexternal, dilated in the middle. 



The meleagrina is distinguished from the avicula, by the dif- 

 ferent form of its shell, which is nearly equivalve, by its never 

 having the tail nor cardinal teeth of that genus, and by the widen- 

 ing of the ligamental facet at the middle part. The aperture 

 for the byssus also occasions a callous, re-entering angle on 

 each valve, which is not found on the aviculee. The meleagrina 

 is not so smooth, and more squamosa than those shells ; its in- 

 ternal pearly coat is sometimes thick, and very brilliant, and it 

 often contains true pearls. The finest of those " costly and 

 beautiful substances I," are found in one species, (M. margan- 

 tifera,) of this genus. 



Type. Melcacjrina margaritifera§. (Mytilus margaritiferus, 

 Limi.) 



Shell subquadrate, rounded above, greenish brown, with 

 white rays ; lamellse longitudinal, imbricate ; the upper ones 

 largest. 



Persian Gulf. 2 Species. PI. II. Fig. 85. 

 Section 2nd. 



Ligament not marginal, contracted into a short space below 

 the beaks, always visible, and not forming a tendinous cord 

 under the shell. 



The shells of this section are well distinguished from those 

 of the preceding by the form and situation of the ligament. 



• S<ifrm colour— yclhw. Lamarck's sixth species. + Masayjic, a Guinea 

 t Uavy. ^ I'euTl-hcaring. 



