INTRODUCTION. 3 



of great interest and importance.^ Althongli isolated and fragmentary records of 

 tlie Pliocene history occnr at Lenham, St. Ertli, in the Cotentin, in north-east 

 Scotland, and probably in the Isle of Man, it is only in the Anglo-Belgian basin 

 and the little-known Crag of Iceland that we have a more or less connected series 

 of fossiliferons deposits from which we may ascertain the character of the molluscan 

 fanna of the seas of north-Avestern Enrope during the period intervening between 

 the Miocene and Pleistocene epochs. No older Pliocene strata are known in 

 Scandinavia, any which may once have existed in that region having been destroyed 

 by the erosion of the great ice sheets. 



It does Wood's memory no discredit to admit that as to some of the Crag 

 Mollusca his nomenclature needs revision ; indeed when we remember that more 

 than sixty years have passed since his Monograph was written, and that so much 

 fresh light has been thrown on the subject, the wonder is that his work requires 

 so little alteration. 



As to certain shells, moreover, our best authorities are by no means unanimous, 

 and one frequently finds in our various Museums the same form under different 

 names. Some species were not figured or were imperfectly described, while in other 

 cases the original figures are not sufficiently clear for correct identification. I 

 have found it, therefore, almost impossible to arrive at satisfactory conclusions 

 as to some of the new material which has come into my hands without obtaining 

 verified specimens, recent or fossil, of the species to which they appeared to 

 correspond. These specimens, with the consent of the Council of the Palseonto- 

 graphical Society, I propose to figure together with the Crag shells, hoping in this 

 way to clear up some doubtful points ; to have given an unsupported opinion of 

 my oAvn Avould have made in many cases " confusion worse confounded." Students 

 will be in possession, at least, of the evidence upon which my identifications are 

 founded, and they will have perfect specimens with which they may compare their 

 fossils in addition to those from the Crag here figured, which are often worn or 

 fragmentary. Where I have been in doubt, I have generally submitted my 

 specimens to some recognised expert. 



The researches upon which Wood's Monograph was principally based were, 

 on the one hand, those carried out by himself and others in the Coralline Crag, 

 the fossils of which are in a specially perfect state of preservation" ; and on the 

 other, in the Red Crag of the region lying between the rivers Orwell and Deben, 

 of the somewhat newer deposits of the Butley district and the Icenian Crag of 

 Norfolk and Suffolk. 



The important beds of Crag at Walton-on-Naze in Essex seem to have been 

 but imperfectly known at that time, less than 150 species from the latter place 



^ It does not seem improbable that other Crag localities might yield results similar to those 

 obtained at Little Oakley if worked in the same manner. 



- Most of Wood's specimens from the Coralline Crag were obtained from one pit at Sutton. 



