102 Mr. H. E. Strickland on the genus Cardinia. 



which had been used four years before by M. von Meyer for a 

 genus of Mammals. 



It appears from this historical statement, that as M. Agassiz 

 was the first to publish the characters of the genus, so his generic 

 name Cardinia must supersede all later ones. 



Some authors have been disposed to extend the geological 

 range of this genus, by including in it those numerous species 

 from the coal-measures which Sowerby and most other palaeonto- 

 logists have regarded as true Unionidce. Whether Agassiz ori- 

 ginally proposed this extension of the genus I am not aware, 

 having never yet been able to meet with his translation of the 

 ' Mineral Conchology/ in which the group is first defined ; but 

 in his last work on the subject, the ' Etudes critiques sur les 

 Mollusques Fossiles/ he seems to regard Cardinia as exclusively 

 confined to the lias and lower oolite. De Koninck however, in 

 his ' Description des Animaux Fossiles du terrain houillier de la 

 Belgique/ classes these coal-measure shells as Cardinia, and pre- 

 fixes a definition of the genus which seems to be chiefly copied 

 from De Christol's definition of Sinemuria, and we may therefore 

 conclude that De Koninck had not been able to examine the in- 

 terior of the fossils which he describes. He seems to have made a 

 compromise between the real characters of Cardinia and the er- 

 roneous statement of De Christol as to the internal ligament ; for 

 he says that the shell had two ligaments, one internal and the 

 other external, a statement which I believe to be wholly incorrect. 



Capt. Thomas Brown also seems to regard the coal-measure 

 fossils as genencally identical with the lias ones, since he has de- 

 scribed, under Mr. Stutchbury's name Pachyodon, no less than 

 twenty-six species of shells from the coal-measures, which he has 

 illustrated with very accurate figures in the f Annals of Natural 

 History ' for Dec. 1843, and in his own ' Fossil Conchology of 

 Great Britain/ plate 73. 



There are however many reasons for regarding as doubtful the 

 supposed affinity between the Unioniform shells of the coal-mea- 

 sures and the true Cardinia of the lias, although it must be ad- 

 mitted that there is much general resemblance in their external 

 forms. In the first place, I believe no author has yet seen or de- 

 scribed the interior of any of the coal-measure shells, and there is 

 consequently no positive evidence whatever as to the structure of 

 their hinges. Secondly, although the general characters of the 

 muscular and pallial impressions, as exhibited by the casts in both 

 these sets of species, are very similar, yet in the coal-measure shells 

 the muscular impressions are much smaller and shallower than 

 in those of the lias, and the lateral teeth, if present at all, are evi- 

 dently much less developed. Thirdly, in conformity with this 

 greater feebleness of the connecting muscles, we find that the 



