vill INTRODUCTION, 
gathered from these details, that in undertaking the present work, the authors have neces- 
sarily, toa great extent, entered upon an unexplored field of study,—have been compelled 
to investigate the relations of forms which, in very many instances, have only recently been 
brought under their notice, and respecting whose analogues some doubt or difference of 
opinion may occasionally exist: with a sincere desire to avoid error, they have in every 
instance rejected species of which the examples were imperfect or doubtful. 
It is with pleasure and gratitude they acknowledge the assistance which they have 
received in the prosecution of their task, and their thanks are especially due to Professor 
Edward Forbes, for his valuable memoir on the Echinodermata; to D. Sharpe, Hsq., for his 
copious notes on the Nerinez, and other valuable suggestions ; to Wm. Bean, Esq., of Scar- 
borough ; to M. Bouchard, of Boulogne ; to Professor Tennant, F.G.S.; to S. V. Wood, Esq., 
F.G.S.; to Professor Buckman; to — Bravender, Esq., of Cirencester ; and to J. Bentley, 
Esq., of Stamford, for the loan of specimens for comparison and figurmg: to M. A. 
Buvignier, of Verdun, for his little work on the *‘ Oolitic Fossils of the Ardennes ;’—also 
for the opportunities afforded them in consulting the important collections of the Viscomte 
D’Archiac; J. Baber, Esq., F.G.S.; J. S. Bowerbank, Esq., F.R.S.; J. G. Lowe, Esq. of 
Chippenham; Rev. P. B. Brodie, F.G.S.; E. H. Bunbury, Esq., M.P., F.G.S.; S. P. 
Pratt, Esq., F.R.S.; and to Professor E. Deslongchamps, of Caen, for his obliging kindness 
in forwarding to them a-suite of specimens typical of some of the species figured by him 
in a series of memoirs, containing many valuable observations, published in the seventh and 
eighth volumes of the ‘Mémoires de la Société Linnéenne de Normandie ;’ as well as to 
J. de Carle Sowerby, Esq., for the loan of many of the original specimens described in the 
‘ Mineral Conchology ;’ and to G. R. Waterhouse, Esq., and S. P. Woodward, Esq., for the 
facilities afforded to the authors in their examination of the species contained in the National 
Collection. ‘To the artists, Messrs. Bailey and C. R. Bone, of the Ordnance Geological 
Survey, the authors tender their acknowledgments for the pains they have taken in the 
general accuracy of the lithographs. 
