been rendered as concise and clear as possible. It is hoped 

 that no essential characters are omitted, and that those living 

 authors, whose proposed generic distinctions have been passed 

 over in a few words, will not have to complain of want of 

 justice in the attempt to interpret their meaning. 



In most cases the generic name will be found accompanied 

 by its derivation. This has been done, in the hope of assisting 

 the memory by associating the meaning of a term with some 

 peculiarity in the thing described. At the end of each de- 

 scription of a genus, some general observations occur, pointing 

 out the principal character which distinguishes it from others, 

 to which it is nearly allied ; and also stating the geographical 

 or geological distribution and habits of the animal. 



The above descriptions and definitions are illustrated by a 

 series of plates, containing above 500 etchings of nearly as 

 many proposed or established genera, arranged in Lamarckian 

 order, so as to show at a glance all the generic forms of each 

 family. And, although from their number, they could not be 

 very highly finished, it is hoped that they will be found cha- 

 racteristic. 



The compiler cannot replace his pen without acknowledging, 

 with filial gratitude, the kind assistance of one who has sacri- 

 ficed much of his time in bringing his knowledge and expe- 

 rience to bear upon the correctness and utility of this humble 

 attempt to remove some of the difficulties to which the com- 

 mencement of this, as well as of every other study, is exposed. 



