KIDSTOX: THE FLORA OK TIIK CARBONIFEROUS PERIOD. 191 



stalk, or cuneate, and even almost tiiiform. Nervation radiating 

 from the base of the pinnule and frequently dichotomising. 

 The cliief genus is Sphenopteris Brongt. 



Spiienopteris Brongt. The general characters of one of the 

 sections of the ferns commonly included in Sphenopteris is well 

 represented by Sphenopteris obtusiloba Brongt. (Plate XXV., 

 fig. 1). The pinnules are oval entire, lobed, or divided into 

 3-5 segments — their form varying according to their position on 

 the i)inna. The dichotomising veins radiate fan-like from the 

 base of the pinnules (Plate XXV., fig. la). 



Anotlier section of Sphenopteris has pinnules with more or 

 less cuneate segments, of which Sphenopteris furcata Brongt. may 

 be taken as a typical representative (Plate XXVII., fig. 2). 

 The segments of the pinnule are narrow, linear, with a veinlet 

 running into each tooth (Plate XXVII. , fig. 2a). In both of 

 these sections there are some species with very small pinnules. 



Although one must be very careful in generalising, still it 

 seems as if tlie linear or cuneate pinnuled forms were more 

 characteristic of Lower Carboniferous rocks, while those with 

 rounded lobed pinnules were more typical of the Upper Car- 

 boniferous. Both types, however, occur together in all the 

 divisions of the Carboniferous Formation. 



Many species originally included in Sphenopteris have had 

 special genera provided for their reception. In some cases the 

 characters are derived from the mode of division of the pinnje 

 — characters dependent on the vegetative system. It appears 

 to me very doubtful if any real advantage is derived from the 

 creation of such genera, as they cannot be regarded as other 

 than provisional, and personally I prefer retaining the ferns 

 placed in these genera in Sphenoptej-is. As examples of the 

 genera to which I refer, Palmatopteris Potonie (of which 

 Sphenopteris furcata is the type), and Diplothmema Stur may 

 be mentioned. 



The other class of genera which have been taken from 

 Sphenopteris Brongt. hold, however, a very different position, as 

 they are founded on characters which are derived from their 



