viii INTRODUCTION. 



Natural History,' upon the Freshwater Formation of the upper Tertiaries at 

 Maidstone, in Kent. The Period to which this bed belongs has not yet been satis- 

 factorily determined. 



In the eighth volume of the ' Magazine of Natural History,' 1839, Mr. W. Bean 

 gave an account of a deposit at Bridlington Quay, whence some of the shells I have 

 figured were obtained. 



In 1840 Mr. John Brown, of Stanway, communicated a Paper to the ' Magazine of 

 Natural History,' describing a Lacustrine deposit at Clacton, on the coast of Essex, 

 which is probably the Freshwater equivalent to the Red Crag Formation. This 

 gentleman also printed and privately distributed a list of Crag Shells, obtained by 

 him from a place called Beaumont, in Essex. In this list, however, there are not 

 the names of any species but such as have been obtained at Walton-on-the-Naze by 

 myself; and as I have not been able personally to inspect the locality referred to by 

 Mr. Brown, no special reference has been made to it. 



In December, 1843, Professor Henslow read a Paper before the Geological Society, 

 describing fossils from the Crag at Felixstow, which he considered to be the Co- 

 prolitic remains of whales ; and introduced a notice respecting some tympanic bones, 

 which were referred to the genus Balaenodon by Professor Owen. 



As early as the year 1812, Mr. James Sowerby, senior, commenced the ' Mineral 

 Conchology,' which for a long series of years has been almost the only publication 

 by which British fossil shells of all Periods have been made known to the public in 

 this country ; and this work has been ably continued by his son, Mr. James De 

 Carle Sowerby, to the present time. 



The first portion of the present work contains descriptions of univalve shells, 

 or the calcareous remains of Gasteropodous Molluscs. The great variety of forms pre- 

 sented by the testaceous coverings of this class of animals, depends upon the height 

 or length of the cone. This ranges through every degree of angularity, from the 

 nearly discoidal form exhibited by some of the Patelliform species, in which the cone 

 is so depressed as to form an angle, from the vertex to the margin, of 170 degrees, to 

 that of an elongated tube, extended in some cases so much as to become nearly 

 cylindrical, and twisted into almost every conceivable form of spiral, for the con- 



