vi PREFACE. 



noted 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 occa- 

 sionally appear in the numbering of the plates. Thus 

 in Plate I. we pass from No. 27 to 29 ; in Plate II. from 

 17 to 19, 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 num- 

 ber engraved on the plate. Thus -f 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 -f an 

 inch and three-quarters ; b two inches ; c three inches, 

 and so on : n denotes shells of the natural size ; and m 

 such as are magnified. Thus in Plate I. figure 15 is an 

 inch long; fig. 16, an inch and a quarter ; fig. 4, an inch 

 and a half; fig. 1, two inches ; fig. 27, three-quarters of 

 an inch ; fig. 29, the natural size. In the genus Nautilus, 

 Plate 13, all the figures, except three, are magnified. 



