SPHENOPHYLLEAE 



87 



Sphenophylleae, is characteristic of the Carboniferous 

 formation, and occurs throughout its whole extent, 

 appearing also in the 

 Permian immediately 

 above it, but scarcely 

 reaching the Triassic. The 

 slender stems of Spheno- 

 phyllum were ribbed ; the 

 ribs did not alternate in 

 successive internodes, but 

 ran straight on through 

 the nodes ; in like manner, 

 the leaves of successive 

 whorls were not alternate, 

 but superposed, a point of 

 great importance among 

 the distinctive characters 

 of Sphenophyllum. In the 

 typical species, on which 

 the genus was founded, 

 the leaves, usually six in a 

 whorl, were wedge-shaped, 

 with an entire or toothed 

 margin (Fig. 35). It was 

 soon found, however, that FlG , 3S 

 the wedge-shaped form of 

 leaf was not universally 

 present. In very many 



cases the leaves were dichotomously divided into 

 narrow lobes, and in some we find a whorl of per- 

 fectly simple narrow leaves, which may be regarded 

 as corresponding to the segments of a smaller 



Sphenophyllum, sp. Branched 

 stem, bearing linear and cuneate whorled 

 leaves on different parts. The branch a 

 terminates in a long and slender cone. 

 Half nat. size. After Stur. 



