36 FILICIN ©. 
distinguish certain types of fern fronds, separated from one another 
by the characters of their nervation; these have been, and still 
are to a large extent, the accepted terms which are used in 
speaking of Paleozoic specimens. They are accepted on the 
understanding that in making use of such names we are merely 
admitting our imperfect knowledge, and, as the only possible 
basis of classification, make use of a system which is thoroughly 
artificial. Ettingshausen, whose works on the venation of the 
vegetative organs of plants are so widely known, attempted a 
classification of living ferns on the same lines as those which 
are followed in dealing with fossils.1 That such a system of 
arrangement rests on a foundation utterly imsecure has been 
pointed out by Stur in his classic work on ‘ Die Carbon-Flora 
der Schatzlarer Schichten.”? He shows how such a genus as 
Polypodium affords examples of eleven of Ettingshausen’s venation 
types, and how the same genus has three types in common with 
Acrostichum, four with Pteris, four with Asplenium, and six with 
Aspidium. Then again the venation type Sphenopter’s occurs in 
twelve genera and three families. Hence it must be admitted 
that the genera which are based on characters of venation alone 
are essentially provisional, and, if recognized as such, are of 
extreme value until increased knowledge places us in a position 
to determine the family to which a fossil fern belongs. 
The custom of giving recent generic names to fossil ferns is 
one which several writers have frequently adopted in dealing 
with Mesozoic and Tertiary plants. This practice, I am inclined 
to think, has been followed too commonly; and the result has 
been that among the more modern fossil ferns we find a large 
number of species spoken of by the names of living genera, to 
which they have little or no claim to relationship. In speaking 
of fossil algee attention has been drawn to the great danger which 
necessarily accompanies this use of modern names; the same 
remarks apply in the present instance with equal weight. Surely 
there ought to be good evidence at our command before a fossil 
fern is designated by such names as Dicksonia, Thyrsopteris, 
Aspidium, etc., and thus presumably an authenticated occurrence 
put on record of any of these genera at a certain locality and 
1 Farnkrt. Jetztwelt. Vienna, 1865. 
* Abh. k.-k. geol. Reichs. vol. xl. Abth. i. 1885. 
