148 Tne American Geologist. September, 1896 
And here we approach an important question of principle. 
The larger categories in botany and zoology are almost exclu- 
sively based on the investigation of forms that still exist; 
and it is only in those divisions where the fossil forms sur- 
pass the recent ones, in number or in variety of organization, 
that they, too, have been taken at all into account. As a rule 
it has been thought good enough to wedge in the extinct or- 
ders or families between the groups erected by the botanists 
and zoologists. Thus the foundations of the system remain 
intact. It is only recently that attempts have been made to 
reconstruct individual divisions of the zoological system, to 
a certain extent from below, on a paUeontological basis. 
Thus, Scudder has established a sub-class, Paheodictyoptera, 
for all paUeozoic insects, because they possess a series of com- 
mon, indifferent characters and show as much morphological 
correspondence one with another as they do with the later 
Orthoptera, Neuroptera and Hemiptera, whose predecessors 
can already be clearly recognized among the paheozoic forms, 
although they have not yet attained the complete differentia- 
tion of their later descendants. Could we resurrect the nu- 
merous genera of the Puerco beds and place them among our 
fauna of to-day we should doubtless arrange them in one 
common order, more or less corresponding to the marsupials; 
for, like the marsupials, they possess characters that, at all 
events, point in the direction of orders more clearly differen- 
tiated later on, in which orders we are at present accustomed 
to enroll them. 
If the zoological and botanical systems were now to be 
created for the first time, they would in many respects prob- 
ably assume a different appearance. They would have to 
represent clearly the natural relationship and the derivation 
of the organisms. The geologically oldest representatives of 
any of the larger assemblages, which are as a rule also the 
most generalized and most primitive, would have to be united 
under a special name and would be regarded as the common 
root of the orders, families, genera, etc., proceeding from 
them. But it is only in a few cases that palaeontology could 
furnish the materials required for a reform of this kind. As 
a rule, and especially among the invertebrates, the primitive 
generalized types are missing, and we should be obliged to 
