PBEFACE. 



WHEN I had completed my first Supplement to the " Crag Mollusca " in 1872-4, 

 I did not contemplate ever attempting any further addition, as even if I had desired 

 to make any, my advanced years rendered it improbable that I could accomplish such 

 a thing. The discovery, however, of some shells at Boy ton, one of them (Fusus Waelii) 

 apparently identical with a shell from older beds in Belgium and Germany, and 

 two others (Murex Eeedii, and M. pseudo-Nystii) presenting an approach to certain 

 Murices of the same older beds, were of such interest as to render their represen- 

 tation by figure and description desirable, for if, as is probable, they lived in the 

 Coralline Crag sea, they furnish evidence of a nearer connection of that sea with 

 the Miocene than modern opinion has been inclined to grant. 



I was thus induced to enter upon a second Supplement, which I at first thought 

 might be confined to a single plate, but when this had been engraved I reflected 

 that as so many species had been introduced into lists of Crag shells, which I had 

 not introduced into my first Supplement from a feeling that the authority for them 

 was too scant or doubtful to justify it, or, in some instances, from a feeling that 

 the identity was erroneous, it was incumbent on me to present to geologists by 

 figured representations the evidence upon which these introductions were based < 

 This, therefore, I have endeavoured to do, and by it have, perhaps, exposed myself 

 to the objection that the plates have been extended to but little purpose, as many 

 of the so-called new species are either very doubtful in themselves, or are merely 

 derivatives from destroyed beds ; though most of these beds probably belong either 

 to the Coralline, or to some still older part of the Crag; i.e. to the oldest Pliocene, 

 now present in Belgium. To such objections my answer would be that I have long 

 felt that the introduction of so many new species into Crag lists, either from the 

 unsatisfactory evidence of a single specimen, or from the (in my view) improper 

 identification made, or from the presence of mere derivatives, must produce among 

 geologists, especially those abroad, very erroneous conceptions of the Crag Fauna ; 

 and that it was to the advantage of science that these evidences should be placed 

 in an appreciable form before the scientific world. 



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