Since 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 subdivided according to their natural groups, and each distinguished as a genus or subgenus by its peculiar 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 genera the new ones have been separated.

[Pg vi]
[Pg vii]