SPHENOPIEEIS. 105 



belonging to several families, are necessarily included in the 

 definition which he has given.' 



Since Brongniart's time Sphenopteru has been subdivided by 

 various -writers into separate subgenera or genera. In such cases 

 where the subdivision has been founded upon characters which are 

 clearly of taxonomic value, the new terms proposed ought to be 

 accepted as useful additions towards a rational classification of fossil 

 ferns. On the other hand, to multiply terms for genera founded 

 on characters admittedly of doubtful value, is hardly calculated to 

 advance our knowledge of the botanical affinities of fossil forms. 

 As an instance of such grouping we may refer to Schimper,^ who 

 has instituted several types of Sphenopteris, based on resemblances 

 of the purely vegetative organs to the fronds of existing genera. 

 TJntil we know more of the fructification of fossil ferns, it is 

 safer, and more consistent with our endeavours to avoid further 

 unnecessary increase in the list of generic terms, already sadly too 

 long, to make use of such genera as Sphenopteris under the older 

 and more comprehensive sense. As evidence accumulates which 

 is of real value, we shall sooner or later be in a position to make 

 use of those standards of comparison which, in the case of 

 recent ferns, are recognized as the most trustworthy bases for 

 family and generic classification. 



Por convenience sake the provisional genus Sphenopteris may be 

 defined as follows : — 



Herbaceous plants, fronds hi- or tripinnate, venation of the types 

 Sphenopteridis, Ctenopteridis, or Cyclopteridis ; pinnules lobed, 

 dentate or entire, tapering towards the point of attachment to 

 the rachis, form varied, but frequently cuneate. 



Whilst making use of a definition such as this we must bear in 

 mind that Sphenopteris, as a genus, is founded on general characters, 

 and such as recur in distinct families and genera. Tontaine,' in 

 the " Potomac Plora," has called attention to the provisional 

 nature of this genus; but, unfortunately, in his frequent use of 

 recent generic names there does not always appear to be sufficient 

 data to warrant a departure from the older, if less scientific, 

 terminology. 



' Hist. veg. fosB. p. 169. 



* Trait, pal. veg. vol. i. 1869, p. 371. 



' Potomac Flora, p. 89. 



