131 



8vo, 1787 ; ' Humphrey's Catalogue of the Calonne Collection,' 8vo, 

 1797 ; and the ' Museum Boltenianum,' 12mo, 179S (which was re- 

 printed at Hamburg in 1819, but neither edition has occurred to me). 

 These catalogues foreshadow the genera which have been since formed 

 and generally adopted, but as they are mostly without characters, or 

 with only very slight ones, I have not adopted the generic names 

 they have given, except where their groups exactly corresponded with 

 those which are now used, and to which new names have been 

 applied, as for example Neritella for Neritina, &c. ; or where the 

 name used by the more modern author was necessary to be changed, 

 because it had previously been used for some other genus of Mol- 

 lusca. 



I have been as careful as I could to give the proper dates of the 

 various genera, especially where there was any doubt about the pri- 

 ority of a name ; but where there was no doubt, as for example in 

 the genera named by Lamarck between the publication of his 

 ' Systeme ' and his ' Histoire,' I have been satisfied with giving the 

 dates of the volume of the latter work, without searching out the 

 exact date of the publication in Lamarck's various papers ; and I have 

 followed the same course with regard to De Blainville's genera which 

 appeared before the date of his ' Manuel ' in the different volumes of 

 the ' Dictionnaire des Sciences Naturelles ' ; but there are certain 

 works the dates of which it is very difficult to ascertain, such for 

 example as Ferussac's, which have no date marked on them. Others, 

 such as D'Orbigny's ' South America,' the publication of which was 

 spread over eleven years, from 1835 to 1846, and some other works 

 of this author, are in the same predicament, the plates often appear- 

 ing irregularly, and the text sometimes not till near the completion 

 of the work. The same difficulty occurs in some of our English 

 works, as Sowerby's ' Genera' for example ; in these cases the dates 

 assigned can only be regarded as approximative. 



I have nearly confined the list to the genera which occur in the 

 recent state : first, because, though I have paid considerable attention 

 to fossil shells, 1 am not so well acquainted with them as with the 

 recent ones ; secondly, because the genera of fossil shells, which must 

 depend on the study and organization of the recent ones, are not 

 so well understood as those which now occur. And the increase in 

 the knowledge of the animal gives us more and more reason to 

 distrust our conclusions with regard to arrangements founded on the 

 study of the shell alone, for it is impossible amongst the recent shells 

 to distinguish the following genera : — 



Tectum (Lottia) from Pate/la ; 



Ancylus ,, Siphonaria ; 



Scutella ,, Patella ; 



Philippia ,, Solarium ; 



Vermetus ,, Serpula ; 



Dentalium ,, Ditrupa ; 



though the four first each belong to different families of Mollusca, 

 and the two latter are Mollusca, and their resemblances Annelides. 

 The knowledge of the animals of Nautilus and Spirula now renders it 



B 



