366 FILICALES [CH. 



Stur founded the species Thyrsopteris schistorum^ are too im- 

 perfectly preserved to warrant the use of this generic name. 

 Goeppert^ in 1836 instituted the genera Cyatheites, Hemitelites, 

 and Balantites for species of Carboniferous ferns believed to be 

 closely allied to recent Cyatheaceae, but a fuller knowledge 

 of these types has clearly demonstrated that in all cases the 

 reference to this family had no justification. 



The Upper Carboniferous species Dicksonites Pluckeneti, of 

 which SterzeP described fertile specimens in 1886 as possessing 

 circular sori, has since been shown by Grand'Eury* to be a 

 Pteridosperm bearing small seeds. In Sphenopteris (Biscopteris) 

 cristata (Brongn.) Zeiller^ has described sori very like those of 

 Cyathea and Alsophila, but differing in the exannulate sporangia: 

 this species, like so many of the Palaeozoic ferns, is probably more 

 akin to the Marattiaceae than to the Cyatheaceae. 



We have as yet no satisfactory evidence of the existence of 

 the Cyatheaceae in Palaeozoic floras. It is not until we reach 

 the Jurassic period that trustworthy data are obtained. Kaci- 

 borski' has identified as Cyatheaceous fertile Jurassic fronds 

 from Poland, but his figures are inconclusive. In Alsophila 

 polonica it is not clear whether the annulus is vertical or oblique, 

 and in another supposed member of the family, Gonatosorus 

 Nathorsti, in which the indusium is described as bivalvate, 

 there is no proof of affinity to Cj^atheaceae. 



In attempting to decipher the past history of the Cya- 

 theaceae it is important to remember the close resemblance 

 between the fertile segments of some species of Davallia 

 (Polypodiaceae) and those of Dicksonia (fig. 229, C, D, p. 294). 

 Unless the sporangia are well enough preserved to show the 

 position of the annulus, it is frequently impossible to feel much 

 confidence in the value of the grosser features, such as the 

 reduced lamina of the fertile segments and the form of the 

 sori. It is, however, probable that the widely-spread Jurassic 

 species Coniopteris hymenophylloides is correctly referred to the 



1 Stur (75) A. p. 19, PI. x. figs. 1, 2. 



2 Goeppert (362) A. pp. 319, 320, 329. 



3 Sterzel (86). 4 Grand'Eury (05). 



= Zeiller (06) Pis. ii. in. " Eaciborski (94) A. PI. ix. 



