INTRODUCIIOir. Vll 



strating the value of fossil evidence in the identification of strata. It 

 contains specimens figured in ' Strata identified by Organized Fossils,' bj- 

 Dr. William Smith. Purchased in 1816. 



Sowerhy C'ullection. — Formed by the late Messrs. James and J. de Carlo 

 Sowerby, joint authors of the ' Mineral Conchology,' in which the speci- 

 mens are figured and described. Purchased from Mr. J. de Carle Sowerby, 

 1861. 



Wetherell Collection. — Obtained chiefly from the London Clay of High- 

 gate and surrounding localities, and purchased through Mr. J. Tennant 

 from the late Mr. Nathaniel T. WothereU, F.G.S., in 1871. 



Wise Collection.— Consists of a few shells collected in the Middle 

 Eocene of Hampshire, and figured in Wiso's ' New Forest.' Presented by 

 J. E. Wise, Esq., 1876. 



Four of these Collections are kept separate as " Type Collections," viz., 

 the lirander, Sowerby, Wm. Smith, and F. E. Edwards, the remainder 

 being incorporated and arranged in the cases containing the general series 

 of British Lower Tertiary MoUusca. 



It is necessary to state that no sections or subgenera have been intro- 

 duced into this work; where characters have been deemed of sufficient 

 importance to merit their recognition, they have been treated as genera. 

 It is thought that this rendering of the subject will greatly tend to 

 simplify and to divest it of its otherwise complicated divisions. 



Following on the synonymy of each species are given the different 

 horizons which have yielded them. The terms employed for these are 

 those adopted in the maps and memoirs of the English Geological Survey, 

 chief among which may be mentioned Mr. W. Whitaker's ' Geology of 

 London,' 1889, and the late Mr. H. W. Bristow's ' Geology of the Isle of 

 Wight,' 2nd edition, edited by Messrs. C. Eeid and A. Stralian, published 

 in the same year, both of which works contain the latest digest on the 

 geological conditions of the London and Hampshire areas. The Oligocene, 

 as an extra division of the Tertiary system, is now fully recognized in this 

 country, and includes all those deposits lying between the base of the 

 Headon Hill series, excluding the Headon HiU Sands (which are of Barton 

 age, and consequently form the topmost part of the Upper Eocene), and 

 the whole of the Hempstead Beds, and which have their development in 

 the northern half of the Isle of Wight and in certain localities of Hamp- 

 shire (Brockenhurst &c.). It was a term first proposed by Prof. Beyrich 

 in 1854 for an extensive series of strata in Germany (Mayence Basin &c.), 

 which presented a fauna intermediate in its characters between that of 

 the Eocene and Miocene formations. 



The classification of these strata in other continental localities has been 

 mainly carried on by Sandberger, Mayer, Ileuevier, and von Kiinen, 



