PRF.FACK TO THE INDFA'ES. 



of the science generally, and particularly a better acquaintance 

 with the fossil shells themselves, through more perfect specimens, 

 have rendered some alterations in the nomenclature absolutely 

 necessary, especially in the generic names; but the changes made 

 in these indexes are as few as they could consistently be, because 

 the frequent changing of names is a source of great perplexity. 

 The alterations in the specific names are not numerous: when they 

 occur they are pointed out. One or two new genera are proposed, 

 and their characters given. 



The Geological Index will, in some cases, be found at variance 

 with the former text; where that is the case, the difference has 

 arisen from some discovered error in the locality given, or has 

 been made upon authority which cannot be questioned: still the 

 Author fears many errors remain, which the length of time 

 he has had the indexes in hand has not removed, and mostly 

 arise from an inaccurate knowledge of the places from whence the 

 fossils are stated to have come into his collection. The additional 

 localities given are much fewer than he anticipated, the Au- 

 thor finding from experience that he could not trust implicitly 

 to the lists hitherto published, or supplied by his friends, in 

 consequence of sufficient attention not having been always paid 

 to specific distinctions: he has therefore principally depended 

 upon one or tw^o collections within his reach, and upon con- 

 tributions to his own, for those additional localities. The Au- 

 thor has received in this department much assistance from the 

 extensive knowledge of a practical geologist, who has aided him 

 in correcting the references to formations: to him, to H, H. Good- 

 hall, Esq., and to many friends from whom he has had both in- 

 formation and specimens, he begs thus publicly to tender his sin- 

 cere thanks, and to express a hope that they will continue their 

 assistance so as to enable him to improve in the projected con- 

 tinuation of this w^ork. 



To the public the Author feels deeply indebted, and cannot re- 

 frain from declaring his gratitude for the encouragement bestowed 

 upon a work commenced by his lamented father, and in the con- 

 tinuance of which he himself has incurred so much responsibility, 

 and also to crave consideration for errors towards those who alike 

 were more conversant with the pencil than the pen, and wdio 

 have sacrificed much tow^ards the advancement of their favourite 

 sciences. 



Camden Town, 

 July, 1835. 



