VI PREFACE. 



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. 



