131 



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

 1797 • and the ' Museura Boltenianum.' 12mo, 1798 (which was re- 

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

 Seeclloguesforeshadowthegenerawhichhavebeensxncefo^^^^ 

 and generallf adopted. but as they are mostly without characters, or 

 tith only very slight ones, I have not adopted the genenc names 

 7heY Ze given. except where their groups exactly corresponded with 

 tho«e whi!h are noi used, and to which nevv names have been 

 applied as tbr 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- 



^""'l have been as careful as I could to give the proper dates of tlie 

 variou-' -enera, especially where there was any doubt about the pn- 

 or^ Jfa nan.; ; but where there was no doubt. as or exa-p k m 

 the^enera named by Lamarek between t^e pubhcation of lus 

 ' Syslme' and bis • Histoire,' I have been satisfied .vith giving the 

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

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

 S ved the šame course with regard to De Blamville's genera ^^^lch 

 anpeared before the date of bis ' Manuel ' m the different volumes of 

 the DTctionnaire des Sciences Naturelles'; but there are certam 

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

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

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

 sp ad over lefeZyears, from 1835 to 1846. and some other works 

 of thTs author. are in the šame predicament. the platės often appear- 

 L i regulari;. and the text sometimes not till near the completion 

 of the work7 The šame difficulty occurs in some of our Enghsh 

 lrk« as Sovverby's ' Genera for example ; m these cases the dates 

 assioTied can only be regarded as approximative. _ 



KL nearly confined the list to the genera wh.ch occur in the 

 recent statė : first, because. though I have paid considerable attent on 

 Jo fos«il shells. I am not so well acąuainted with them as with the 

 recent ones ; secondly. because the genera of fossil shells. ^-hich mušt 

 depend on ihe study and organization of the recent ones. are not 

 so ^^'eU understood as those which now occur. And the increase m 

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

 distrust our c^nclusions ^.ith regard to arrangements founded on the 

 Sy of the Shell alone. for it is impossible amongst the recent shells 

 to distinguish the follo^nng genera :— 



Tectura (Lottia) from Patfia ; 



Ancylus ,. Siphonaria; 



Scutella „ ^«f^'^«: 



Philippia Solanum; 



Vermetus „ Serpula; 



Dentalium ., Ditrnpa: 



thon^rh the four first each belong to diflferent famJies of Mollusca 

 «nd the two latter are Mollusca. and their resemblances Annehdes. 

 The kuo Sedge of the animals of Nautilus and Spirula now renders it 



