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TO THIS EDITION. 



oiNCE the original Edition of the present work 

 was published, a gradual and great alteration has 

 taken place in the nomenclature of the genera, 

 occasioned by the old ones being further subdi- 

 vided according to their natural groups, and each 

 distinguished as a genus or subgenus by its pe- 

 culiar name. These names in the present Edition, 

 in order to keep pace with the progress of the 

 science, have been generally adopted, and some 

 new ones introduced. The improved Index, which 

 may be had separately by the purchasers of the 

 former Editions, will point out from what old ge- 

 nera the new ones have been separated. 



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