PRELIMINARY REMARKS. 3 



etages Portlandien. 



„ Kimmeridgien. 



„ Corrallien. 



„ Oxfordien. 



Terrain Jurassique . ( » Callovien. 



„ Bathonien. 



,, Toarcien. 



„ Liasien. 



„ Senemurien. 



We are not struck with the superiority of this newly-proposed arrangement over the 

 one in common use, which we have adopted in the following pages, as it is never advisable 

 to burden science with fresh names when old ones serve the same purpose. To the late 

 Mr. Sowerby and other authors we are indebted for numerous correct descriptions of 

 many species from the Oolitic and Liasic series; but the recent impulse given to the study 

 of Palseontology has brought to light so vast an assemblage of new forms and better 

 representatives of several known ones, that it has been deemed advisable to reconsider and 

 publish, under the form of a series of Monographs, all the old species revised, annexing the 

 new forms due to the exertions of local geologists, who have done so much to advance 

 our knowledge of this and other classes, without whose assistance we never could hope to 

 achieve the laudable ends proposed by the Palseontographical Society and their liberal 

 and learned Secretary. 1 Within the last few years, attempts have been made with more or 

 less success to throw light on the class of shells occupying us at present, through an 

 endeavour to classify them by their general affinities. Our object is simply to treat of the 

 Oolitic and Liasic species, comprising only a few genera, because we confine within more 

 general limits as many characters, said to be generic, which we consider to be only specific or 

 sectional differences, and which future discoveries will tend to generalise. How frequently 

 have gaps existing in the zoological chain of affinities 3 been filled up of late years by the dis- 

 covery of forms unknown to early writers, proving how boundless the field of research is 

 in the kingdom of Nature, and how cautious we should be in assuming the uniform preva- 



1 It is therefore pleasing to me to express my grateful feelings and sincere thanks for the kind 

 and liberal assistance I have received in the preparation of this work from MM. Bouchard, Deshayes, 

 Deslongchamps, Buvignier, Milne Edwards, Valenciennes, De Verneuil, Delessert, De Koninck, Morriere, 

 Chenu, &c. ; from Messrs. Ko'inig, Waterhouse, Woodward, of the British Museum ; Sir H. De la Beche ; 

 Professor Forbes and Mr. Salter, of the Geological Survey ; the Geological Society's Museum ; that of Bristol, 

 &c, where I was allowed to make use of the valuable collections deposited there ; from Messrs. Bowerbank, 

 Walton, Moore, Morris, J. de C. Sowerby, Hugh Miller, Robertson of Elgin, M'Coy, Rose of Swaffam, 

 Riply of Whitby, Marder, Bean and Leckenby of Scarboro', Tennant, Faulkner of Deddington, Buckman, 

 King, Dr. Wright of Cheltenham, Mr. Cunnington of Devizes, Messrs. Lycett, Lowe, Griesbach, and others, 

 who have communicated to me the Palseontological treasures belonging to their respective collections. 



2 For various reasons we have commenced with the species of the Oolite and Lias ; but it is of little 

 importance, as this work is to be composed of a number of distinct monographs. Next year we hope to be 

 able to give the general introduction, in which we shall state our views on the classification and genera. 



