5. Avicula. Lam. M. 



Inequivalved , fragile , 

 base transverse, straight, 

 its extremities advanced 

 and the anterior cau- 

 diform ; a slope on the 

 left valve : beaks small. 

 Fig. 70. 



6. Meleagrina. Lam. M. 



Sub-equivalved, almost 

 a round cornered square ; 

 scaly ; without cardinal 

 edge ; straight ; without 

 anterior tail. Fig. 71. 



( 22 ) 



Hinge linear, 1 car- 

 dinal tooth on each valve 

 under the beak. 



Hinge linear, without 

 teeth. 



Area of ligament mar- 

 ginal, narrowed like a 

 channel, not crossed by 

 thebyssus. (1) 



Area of ligament mar- 

 ginal, long, almost ex- 

 terior, dilated in the 

 middle : A sinus at the 

 posterior base for the 

 byssus, the left valve 

 being narrow and slo- 

 ped. (2) 



(1) Foss. in the London Clay, at Grignon, Bourdeaux. 



(2) The most celebrated species, is the Mytllus margaritiferus of Linnaeus ; the 

 inside is covered with the most beautiful mother-of-pearl, which is employed for 

 ornamental purposes, and its pearls, so celebrated in the East 3 are dived for on 

 the coasts of Ceylon, Cape Cormorin, and the Persian Gulph. It is also found 

 in New-Holland and the Gulph of Mexico, 



A 



