INTRODUCTION. 



In the following paper we have endeavored to bring to- 

 gether the definitions of those genera of the family Attidae 

 which have been generally received, and also of those which 

 are part of the synonymy of the received genera. Up to this 

 time these definitions have been so widely scattered througb 

 different works and periodicals that it has been a matter of" 

 great practical inconvenience to study and to compare- 

 them. It is probably due, in a measure, to this fact that 

 many species have been placed in genera from which a mod- 

 erate regard for the generic definitions would have excluded 

 them; although perhaps a further difficulty may have arisen 

 from a confusion of the two modes of classification, the one 

 based on a type, and the other based on a general definition. 

 To make clear the distinction between these two modes, we 

 quote from WhewelP, " Natural groups given by type, not 



bj definition the class is steadily fixed, though 



not precisely limited; it is given, though not circumscribed; 

 it is determined, not by a boundary line without, but by a. 

 central point within; not by what it strictly excludes, but by 

 what it eminently includes; by an example, not by a pre- 

 cept; in short, instead of a defiaition we have a tijpe for our 

 director. A type is an example of any class, for instance, a 

 species of a genus, which is considered as eminently possess-- 

 ing the character of the class. All the species which have^ 

 a greater affinity with this type-species than with any other, 

 form the genus and are ranged about it, deviating from it in 

 various directions and diff areat degrees." On the other side 

 we have from Mill:' " the next step is to ar- 



' The Philosophy of the Inductive Scieacea, Vol. 1, pp. 476, 477. 



■A System of Logic, pp. 501, 503. Huxley, al-io says: "It is stid, in 

 short, that a natural history class is not cap3.ble of being defined — that 

 the class Rosacea? for instance, or the class Fishes, is not accurately and 

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