xii PREFACE TO THE 



shells composing his genera are very rare, and 

 they could only know them by pictures ; the 

 generic distinctions also are often so minute that 

 they would elude the observations of minds un- 

 practised in scientific details. There is on the 

 contrary something in the simplicity and clear- 

 ness with which the great Swede seized arid de- 

 fined the broad outlines of nature peculiarly suited 

 to the capacities of the young ; and they may be 

 led with very little assistance, to group the shells 

 according to his arrangement, and to draw out 

 from their own observation the generic characters. 

 Nor will an acquaintance with the Linnsean 

 system be without its value, when they may de- 

 sire to study a more perfect classification than 

 his ; they will find the task of subdividing, 

 separating, and arranging very much more easy 

 than if they had to work upon materials altogether 

 new to them ; they will have points established 

 in their minds to which they may compare and 

 attach the new ideas presented : their perceptions 

 will be quickened to discover similarities and dif- 

 ferences ; and they will find many of the dif- 

 ficulties that embarrass the student at the very 

 threshold of science, overcome by their previous 

 lessons.* Some again have objected to the sub- 



* A table of comparison between the two systems of Linnaeus 

 and Lamarck is given at the end of the volume. 



