PINNA. PERNA. AVICULA. O/ 



nearly lateral ; hinge without teeth. The genus 

 Pinna is unaltered. Small crustaceous bodies, 

 resembling the crab, are sometimes found in the 

 shells of the Pinna. 



" Malleacea, 



Crenatula ,.... Rare and little known. 



Perna Chtrea. 



Malleus Ostrea, hammer-oyster. 



A vicula Mytihis. 



Meleagrina My t Has. 



" The first genus is found in the seas of warm 

 climates. The shells are thin and foliated. The 

 hinge of Perna differs widely from that of the 

 oyster. It is linear, formed of sulcated teeth. 

 There is a sinus under the extremity of the hinge, 

 for the passage of the byssus. Compare P. isog- 

 nomon with the common oyster, and you will 

 find few points of resemblance between them. 

 (Plate 5.) Perna epJiippiuni is also a curious 

 species, very pearly within. The hammers are 

 rugged and singular in form. They are all fo- 

 reign, from the oriental seas. 



" AiHcula, or Swallow, so called from tlie resem- 

 blance of the shells to a bird flying, was consi- 

 dered as a single species by Linn;eus. La- 

 marck makes eighteen species in his new genera. 

 Meleagrina has two species. The pearl-bearing 



