PERIPLOMA. 361 



imperfecta, Lam. rugosa, Lam. 



lanterna, Born. subrostrata, Lam. 



papyracea, Say. trapezoides, Lam. 



prisrnatica, Sow. truncata, Lam. 



Genus PERIPLOMA, Schumacher. 



Siphons long, slender, separate. 



Shell transversely ovate, thin, inequivalve, the left valve 

 more ventricose than the right, surface of valves minutely 

 scabrous ; beaks fissured, strengthened within by oblique 

 diverging ribs. Hinge composed of a spoon-shaped, ob- 

 lique or horizontal process in each valve containing the 

 ossicle and cartilage ; ligament external. Anterior muscu- 

 lar impression very narrow and sub-marginal, posterior very 

 small and rounded ; pallial line posteriorly sinuated. 



Syn. Bontia, Leach. Cochlodesma, Couthouy. Ligula, 

 Recluz, not Montagu. Corimya, Agassiz (fossil). 



Ex. P. ovata, B\Orbigny, pi. 96, fig. 2. Shell, P. inre- 

 quivalvis, Schumacher, fig. 2, a, 2, b. 



There does not appear to be any generic difference 

 between Periploma and Cochlodesma, the latter possessing 

 the usual testaceous appendage, or ossicle, peculiar to most 

 of the genera of this family. The species of Periploma 

 are principally inhabitants of the West Indies and the 

 coasts of South America ; the Mya pratenuis of Pultney 

 is from the shores of Europe, and the Anatina Leana of 

 Conrad is from the coasts of the United States. Fossil 

 examples occur in the secondary formations, and constitute 

 the extinct genus Corimya of Agassiz. 



