294 STUDIES IN FOSSIL BOTANY 



spores, is the extreme distinctness of the annulus, 

 which, when cut lengthways (a), quite suggests that of 

 a Polypodiaceous Fern, and contrasts sharply with the 

 small cells of which the remainder of the wall is 

 composed. The annulus was evidently longitudinal or 

 somewhat oblique, rather than transverse ; it agrees in 

 detailed structure with the annulus of recent Ferns, 

 especially in the thinness of the external cell-walls, and 

 the gradual thickening of the radial walls from without 

 inwards ; transverse sections of the annulus show, 

 however, that it was regularly two cells in width, thus 

 differing from that of any recent Ferns. Specimens 

 of this fructification, which I have named Pteridotheca 

 Williams onii, are of frequent occurrence in the coal- 

 balls of the Lower Coal-measures, and the preservation 

 is often remarkably perfect. There is every reason to 

 believe that it belongs to a true Fern, though it would 

 be futile to seek for any near affinities with recent 

 families. 



Postponing any further discussion of the extent and 

 character of the Palaeozoic Fern-flora to the end of the 

 following chapter, we will now pass on to consider some 

 cases in which the anatomical structure is preserved, 

 and affords evidence of Filiciaean affinities. We will 

 first discuss an important group of stems in which the 

 structure appears to be of a Marattiaceous type, 



3. Anatomy — Psaronius. — Among the Fern-like 

 remains from the Permo- carboniferous strata, and 

 especially from their upper beds, specimens resembling 

 Tree-ferns, in habit not altogether unlike those of the 

 present day, are conspicuous. Some of these plants 



