OF THE FOSSIL PLANTS OF THE COAL-MEASUEES. 
677 
Under these circumstances the question which is forced upon our consideration is a 
practical one. I find amongst my sections several well-marked structures which cannot 
be located in any of Corda’s genera. Hence, if I act upon Corda’s method, I must not 
only adopt all his generic distinctions, but even add to the evil by creating several new 
genera. 
I was at first disposed to adopt the latter plan, and had proposed the names of Edraxy- 
lon and Arpexylon * for two undescribed types, and also intended adopting Mr. 
Binney’s name of Stauropterisf for a third one. The reasons already assigned make 
the absurdity of this plan obvious. I have therefore determined to reduce the number 
of these genera, and to adopt one common term for the entire series of what appear to 
be fern-petioles, trusting to time and diligent research to enable us to identify them with 
the several fronds and stems to which they belong, all of which have doubtless already 
received generic names. Of course I exclude from my common genus such names as 
Caidopteris and Psaronius , which represent arborescent stems whose external aspects 
are more or less known, and which consequently are not genera exclusively based upon 
the form of the vascular bundle of the petiole. Nothing better indicates the necessity 
for some such course as that which I propose to adopt than the way in which even Brong- 
niart has classed these petioles or isolated rachis. He divides them into two groups : — 
“ ^Petioles a faisceau vasculaire unique ” and “ **Petioles a faisceaux vasculaires mul- 
tiples.” I shall have to describe examples in which the primary petiole would have to 
be located in one of these divisions and its secondary branches in the other — a condition 
sufficiently common amongst living ferns. 
Corda has embraced a number of these petioles in one family under the name of 
Bachiopteridese. In order to avoid the introduction of new names, I propose to adopt 
the term Bachiopteris, and to include in that genus all the several condensed genera 
adopted by M. Brokgniart from Corda, under the names of Zygopteris , Selenochlcena , 
Selenopteris, Gyropteris, Anachoropteris, P til or acids, Diplophacelus, Calopteris, and 
TempsJcia , as well as my own proposed genera of Edraxylon and Arpexylon and Mr. 
Binney’s Stauropteris. I am fully alive to the inconveniences to which this plan exposes 
us ; but it will be easy to indicate the several forms by provisional specific names. It 
appears almost certain that the stems and petioles which are now represented by the names 
just quoted will be ultimately found to belong to various species of Pecopteris, Neuro- 
pteris, Sphenopteris, and their allies. Consequently all other names can but be provi- 
sional and temporary ones. By adopting the plan proposed we avoid burdening science 
with a number of meaningless genera, based upon characters which have little, if any, 
generic value, and which only possess even specific ones under peculiar limitations, 
such limitations arising from the variations which a single petiole exhibits according 
to the portion of it from which a section is made. 
Transverse sections of the petioles of recent ferns exhibit four common types of 
fibro-vascular bundles: — (1) that in which the transverse section of the bundle represents 
* See Proc. Eoy. Soc., No. 136. t Proceedings of the Lit. and Phil. Soc. of Manchester, vol. xi. p. 69. 
4 Y 2 
