2:2 



Now that [ am convinced of them I have much pleasure in giving the 

 corrections. 



Turton, whose work on the British Bivalves stands next in order of 

 date, has inadvertently united the true Crania and Qrhicula together, 

 giving them the name of Discina : his mistake is however of little 

 importance because he never can be regarded as authority upon this 

 subject. 



I now come to Fleming, " who gives a place to Discina ostreoides of 

 Lamarck, even without good proof of its British origin, for the purpose 

 of rectifying some strange mistakes in nomenclature which have been 

 oommilted in reference to this and the following genus" (which is 

 Criopus, of Poli) but this author who thus makes his appearance, " ex 

 Cathedra, " to set us all right, has neither hit upon the first and great 

 cause of all the errors, nor has he corrected the real errors, and he has 

 moreover made some addition to their number. He does not tell us 

 what are the mistakes that he intends to rectify, we are left to find them 

 out, if we can: but we are to take his version of the matter, without 

 his having condescended to give us a reason for any part of it and we 

 are to conclude, with implicit reliance upon his correctness, that he has 

 rectified every mistake that had been committed by all authors who have 

 written upon the subject down to the time of his advent. We shall now 

 see how he has done this — in the first place he lias adopted Lamarck's 

 genus Discina which ought to have been expunged from the system al- 

 together, and has added to it three fossil species of Orbicula which have 

 been published in the Zoological Journal and in Mineral Conchology : 

 then for the Crania he has used the name Criopus which Poli gave to the 

 animal alone instead of using the name which had long before been 

 given to the shell by Retzius and adopted by all authors, except those of 

 the Linnean School : and then further, without giving any reason, asserts 

 it to be probable that Crania of Lamarck is distinct from Criopus. He 

 also says that I have asserted the Orbicula, of Lamarck to differ only in 

 the greater thickness and irregularity of the lower valve from the type of 

 the genus Criopus of Poli. Whereas, what I have said is this, '• The 

 only difference observable between the specimens (of what I have called 



