Gil 



*fc>3 • 



M l-TT 



Li ~ 



PREFACE. 



I VUHUUMUV 



1 his Manual, like those of the Mammalia and the Orni- 

 thology already published, originated in the notes and 

 drawings collected during a study of the subject, prepa- 

 ratory to a second travel in Africa. I had intended to 

 arrange tLo similar materials for the publication of the 

 Reptiles and Fish before the Mollusca, until a further 

 progress in the study of Geology convinced me that the 

 present Manual was not wanting to the Zoologist alone. 



M. Brongniart has shown that the Formations containing 

 the remains of marine shells, very rarely, and then under 

 peculiar and evident local causes, present those of fresh- 

 water shells ; and that the contrary had been alleged, be- 

 cause Genera containing both marine and fresh-water 

 shells, differing not merely in specific but in generic cha- 

 racters, had not been reformed or subdivided. M. Lamarck 

 acknowledged the justice of the observation, and resumed 

 his labours, which had previously advanced this branch of 

 Natural History considerably towards perfection, by es- 

 tablishing separations of marine, fresh-water, and ter- 

 restrial shells ; but, unfortunately, his Extrait du Cours 

 de Zoologie, published in 1812, contains the mere outline 

 of his system, without the descriptions of the genera; and 

 the 1st and only part (which appeared two years ago) of 

 the 6th volume of his Histoire Naturelle des' Animaux 

 sans V ertebres, without figures, contains merely the three 

 ^ or four first genera of the Univalves, and reminds us so 

 frequently of the melancholy affliction which has now 

 compelled this illustrious Naturalist to depend entirely on 

 the eye-sight of others, that the appearance of the remain- 



