ISOCARDIA. 



Very few recent species of this genus are known ; we 

 have given representations of two of them, the Isocardia 

 Cor, and I. Moltkiana; the I. Cor (Heart Cockle of Col- 

 lectors, Chama Cor, Linn.) is frequent in the Mediterra- 

 nean, and occurs on some parts of the British coasts, 

 particularly in Berehaven, where it grows to a large size ; 

 when in good condition, it has a thickish, dull brown epi- 

 dermis, beneath which the shell is prettily marked with faint 

 brownish zigzag lines : the I. Moltkiana is an East Indian 

 and Chinese shell of far greater rarity — it is transversely 

 grooved, and has a longitudinal anterior keel. Lamarck 

 describes one other recent species. 



Several Fossil species are given in plate 295 of " Sower- 

 by's Mineral Conchology/' one of which is from the London 

 Clay, and another from Kelloway's :* according to Brocchi 

 (Conch. Foss. subap. II. 520) two varieties of /. Cor are found 

 in a fossil state in several parts of Italy ; but as a subject upon 

 which much diversity of opinion exists is here brought into 

 question, we should recommend an attentive and compara- 

 tive re-examination of the fossil with recent specimens, be- 

 fore we come to an absolute decision upon this point. 

 Another fossil species is found at Piacenza, the I. arietina, 

 Lam. We have represented the I. Basochiana (Defr. Diet, 

 des Sciences Naturelles), a new and rare species, found in a 

 yellowish limestone by M. De Basoches de Falaise, in the 

 district of Coutances. We think we may venture to express 

 our opinion that all the fossil specimens published in va- 

 rious books, and existing in various collections, are not 

 distinctly characterized Isocardiae, but only the casts of the 

 insides of other bivalves : the best distinguishing character 

 is in the g-roove formed for the extension of the ligament 

 from the hinge to the umbo. It is incumbent on us to men- 

 tion that in Isocardia, the line to which the mantle is at- 

 tached, passing from one muscular impression to the other, 

 is entire. 



♦ A fossil species also occurs in the " Crojg-," which so nearly resemblesi 

 fBe /, Cor, that we know not wherein the specific difference consists. 



