322 L. Agassiz on Animals in Geological Times. 
Since it is not my intention to enter here upon a special eriti- 
cism of the innumerable errors of this kind, still to be found in 
even modern lists of fossils, I shall not multiply my examples. 
These may be sufficient to show how important a correct generic 
identification of the fossils may be in the estimation of the order 
of succession of organized beings; and I cannot but lament the 
utter want of consideration evinced even by many distinguished 
palzontologists in this respect, who seem to think that the knowl- 
edge of species is sufficient in itself to a proper appreciation of 
the order of creation, and that genera are arbitrary divisions es- 
tablished by naturalists merely for the sake of facilitating the 
study of species, as if the more general relations of living beings 
to one another were not as definitely regulated in all their de- 
grees by the same thinking mind, as the ultimate relations of in- 
dividuals to one another. 
In the third place the natural affinities of genera should be as- 
certained. Unless the genera are referred to the families to which 
they truly belong, unless the rank of these families in their 
respective classes is positively determined, unless the peculiarities 
of structure which characterizes them is taken as the foundation 
geological formations among these animals.- Before it was ascef 
tained that the little animal described by Thompson —— 
tire classes of animals during successive geological ages. #° 
ong as the natural position of Trilobites remained doubtful in 
the animal kingdom, the characters of the prototypes of the class 
of Crustacea could not be appreciated. Who does not see how 
impossible it was for those who classified the Trilobites with the 
' Chitons to arrive at any sound results respecting the gradation 
and order of succession of these animals? Whilst now they 4 
beautifully linked to the Macrura of the Trias, by the gigantic 
Entomostraca of the Devonian and Carboniferous periods. Aga, 
the knowledge of the embryology of Crustacea gives us 2 key 
a correct appreciation of the early appearance of the Macrura 
the late introduction of the Brachyura. ‘The removal of 
Bryozoa from among Polypi to the class of Mollusks, will entirely 
