Natural History of the United States. 327— 
sumed to be a difference of degree; and, on the other hand, that the 
Importance of the form, as the prominent character of families, has been 
entirely overlooked? For, though so few natural families of animals are 
well characterized, or characterized at all, we cannot open a modern 
tise upon any class of animals without finding the genera more or 
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‘ture, and ompare it with that of other families. So form is character- 
oe of families; and I can add, from a careful investigation of the sub- 
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jiatfaunilies cannot be well defined, nor circumscribed within their natural 
; ipa Without a thorough investigation of all those features of the inter- 
Structure which combine to determine the form.”—pp. 159, 160. 
wb re The relations of Genera to the other grades of 
visions are thus presented on pages 162, 163: 
such Writers as are celebrated in the annals of science for having charac- 
terized with particular felicity any one kind of these groups, and I have 
Mentioned Latreille as prominent among zodlogists for the precision with 
xh he has defined the genera of Crustacea and Insects, upon which 
hes Written the most extensive work extant. 
as 
