ONYCHIOPSIS. 57 
portions, sometimes extremely minute portions, of fronds, and all 
placed in the recent genus Zhyrsopterts. One would naturally 
expect that this remarkable assemblage of species, called by the 
name of a unique living genus, should rest on trustworthy 
evidence. The author of these forty species himself admits that 
no fructification has been found; surely this admission will be 
sufficient in itself to make botanists pause before they allow them- 
selves to be lost in contemplation of the wealth of specific form 
displayed by these Potomac plants, or to assume as an established 
fact that Kunze’s solitary species was represented in the Potomac 
vegetation by such a host of ancestors. We may justly ask—Are 
there differences enough, and sufficiently well marked, between 
these numerous varieties to warrant the result arrived at; and, 
secondly, is the evidence at hand strong enough to justify the use 
of the name Zhyrsopteris, or even a modification of it which 
would be suggestive of something not quite so certain and well 
founded ? 
To the first question I am strongly of opinion that the answer 
is a decided negative. It must be admitted that my evidence is 
entirely based on an examination of Fontaine’s figures and descrip- 
tions, and has not the weight of testimony derived from an actual 
inspection of the specimens themselves. To the second question, 
the admission that no trace of a fertile pinna or pinnule has been 
recognized is, I am disposed to think, a sufficient reply. It would 
be a presumption and beyond my province, to attempt to describe 
how many species are represented by the “‘ Thyrsopteris”’ specimens 
found in the Potomac beds; but it is at least possible to indicate a 
few of those cases in which the determinations of Fontaine are not 
such as I feel able to accept. 
The species 7. Virginica' is founded on specimens of the ‘‘pinnee 
of ultimate order,” and the fragments figured might easily be 
included in some of the thirty-nine remaining forms without the 
unnecessary institution of an additional species. Another instance 
of the same kind is afforded by 7. alata, which depends for its 
existence on part of a pinna apparently indistinguishable from 
TL. Meekiana. 
In describing 7. rarinervis? Fontaine refers to it as “one of the 
1 Loe. cit. p. 120, pl. xxiv. fig. 1. 
2 Loc. cit. p. 128. 
