272 STUDIES IN FOSSIL BOTANY 



to an affinity with Marattiaceae, but in others they are 

 of quite a different nature. 



The important form -genus Alethopteris} which 

 comes near Pecopteris in foliar characters, is postponed 

 to a future chapter, because there is reason to believe 

 that all, or almost all, the species belonged to seed-bearing 

 plants. The same remark applies to Neuropteris. We 

 will therefore pass on to another of the great frond- 

 genera, Sphenopteris, the characters of which are as 

 follows : — "Fronds generally tripinnate or quadripinnate, 

 more rarely bipinnate ; pinnules usually small, contracted 

 at the base, with a more or less narrow pedicel, habitu- 

 ally divided into acute or rounded lobes, which are 

 themselves contracted into a wedge towards their base. 

 Nervules simple or branched, forming acute angles 

 both with the median nerve and with their own 

 branches." 2 



Generally speaking, the habit of the species of 

 Sphenopteris, a most heterogeneous group, may be 

 compared with that of members of the recent genus 

 Asplenmm (see Fig. 160, Chapter X.). The Sphenopteris 

 type of frond is of great interest, not only on account 

 of the elegance of its varied forms, but also from the fact 

 that a great variety of fructifications, both Filicinean 

 and Pteridospermous, have been referred to it. 



The genus Diplotmema, Stur, as limited by Zeiller, 3 

 differs from Sphenopteris, only in the fact that the 

 primary pinnae are forked, dividing into two similar 

 branches, each of which is repeatedly subdivided, after 

 the manner of Sphenopteris. 



1 See Chapter XI. Fig. 162. 

 * Zeiller, I.e. p. 30. 3 I.e. p. 37. 



