PREFACE TO THE INDEXES. 
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 two 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 work. 
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 who 
have sacrificed much towards the advancement of their favourite 
sciences. 
Camden Town, 
July, 1835. 
