PREFACE. v 



Each page of the Index is divided into five columns. The first 

 contains the Linnean names : the second, a reference to the page 

 in Gmelin's enlarged edition of the Sy sterna Natures , where the 

 descriptions of such shells as were noticed by that editor will be 

 found. The English names occupy the third column : the fourth 

 refers to some of the principal authors whose figures have an esta- 

 blished reputation ; and in the fifth division will be seen the name 

 of the place where every shell is to be found. 



The figures of Montagu and Donovan have been constantly 

 quoted for the British shells, and where the species is confined to 

 Britain, the word alone is mentioned ; but where it occurs also in 

 other parts of the world, it is denoted by " Britain, &c." Thus the 

 shells that have been observed on our coasts will be immediately 

 detected. 



With regard to the Plates, it must be noticed that several shells 

 have been named by authors without any reference to figures, and 

 which are too obscurely described to be identified. This will 

 account for the gaps which occasionally appear in the numbering 

 of the plates. Thus in Plate I. we pass from No. 27 to 29 ; in 

 Plate II. from 17 to 1Q, and from 21 to 23, &c. It must also be 

 noticed, that in some instances the figures are misplaced, such as 

 No. 23 of Plate I., the engraver having forgotten it till he had 

 finished No. 37. 



As a guide to the comparative size of the different shells, a mark 

 or a letter of the alphabet is added after the number engraved 

 on the plate. Thus + indicates a shell half an inch long ; + three- 

 quarters of an inch ; a an inch; a an inch and a quarter; a + an 

 inch and a half ; a + an inch and three-quarters; b two inches ; 



