li PREFACE. 
genera, have been rendered as concise and clear as possible. 
It is hoped that no essential characters are omitted, and that 
those livings 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 accom- 
panied 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 description of a genus, some general observations 
occur, pointing out the principal character which distin- 
guishes 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 La- 
marckian order, so as 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 characteristic. 
The compiler cannot replace his pen, without acknow- 
ledging, with filial gratitude, the kind assistance of one who 
has sacrificed much of his time in bringing his knowledge 
_and experience to bear upon the correctness and utility of 
this humble attempt to remove some of the difficulties to 
which the commencement of this, as well as of every other 
study, is exposed. 
