PREFACE. 



however, attempted to carry this kind of research beyond its ap- 

 plication to the distribution of British generic and specific mollus- 

 can forms in space. The inquiry as to its bearings on their dis- 

 tribution in duration of time, I commend to the researches of the 

 palEeontologist. The views which I had instinctively formed on 

 the origin of species have gathered strength from the present 

 study. Seasoning from the facts before me, apart from any con- 

 siderations of geology, if such a mode of reasoning in the present 

 state of science may be allowed to have any weight, the conclusions 

 at which I have ventured to arrive do not accord with the theories 

 of Edward Forbes or of Darwin, but seem to point to another 

 solution. 



With the hope of making the work useful to collectors of shells, 

 as well as to observers of the external characters and habits of 

 the mollusk, figures are given of the shell of each species (the 

 upper one when in outline representing the natural size), engraved 

 from drawings on wood by Mr. Gr. B. Sowerby ; and a vignette 

 of a living animal of each genus, drawn and engraved in most 

 instances from nature by Mr. O. Jewitt. Three years have been 

 devoted to collecting living specimens. Where these cotild not be 

 obtained or delineated, recourse has been had to some figures of 

 M. Mocpiin-Tandon, and to some unpublished drawings obligingly 

 placed at my disposal by the Bev. M. J. Berkeley. 



The very characteristic portrait of Citoyen Draparnaud prefixed 

 to the volume, has been engraved on steel by Mr. W. Holl from a 

 photograph of a scarce print in Paris, which, I have reason to be- 

 lieve, is the only likeness extant of the renowned but short-lived 

 Professor of Montpellier. 



