106 AMERICAN FERN JOURNAL 
country under these genera. F ruiting specimens are 
always sought and are of course of the greatest value in 
placing fossil forms. From these characters the follow- 
ing genera have been determined in the later horizons 
with great accuracy: Dryopteris, Asplenium, Onoclea, 
Woodwardia, Adiantum, Dennstaedtia, Onychium, and 
many others. From their characteristic form, combined 
with the characters of nervation, the genera Lygodium, 
Gleichenia, and Sagenopteris, have been determined, while _ 
in exceptional cases the internal structure has been 
found silicified so that thin sections have been cut and 
_ studied as successfully as though it were living; such was 
the Osmunda-like form pani described by the late — 
Prof. D. P. Penhallow S 
After all all have been segregated that admit of identifica- _ 
tion on the ba : tie outline, nervation, or | 
fruiting: character, ‘there remains a considerable number — 
. nye ine accordance with what seems to be their 
ae ity or relationship. Thus, a fern having 
aS certain of the fruit characters of the living Schizaeaceae, 
but not agreeing with any known living species, has been 
a called Paani — aipeache at ay for affini- : 
ties among livi 
- we sea ) backward i in ti 
difficult 
