86 BTTFFORDIA. 



pteris acrodentata, Font., 1 suggested a reference of the English 

 forms to this Potomac species, but, on carefully looking through 

 the large series of specimens in the National Collections, it is 

 impossible to come to a satisfactory conclusion as to where the line 

 of demarcation should be drawn expressive of specific differences. 

 There is undoubtedly a very marked difference between PL VI. 

 Fig. 1 and the specimen represented in PI. IV., but this is rather a 

 divergence suggestive of two varieties than one to be regarded as 

 of specific value. If we had only these two extreme forms to deal 

 with, there would be no hesitation in speaking of them as distinct 

 species, but, as already pointed out, we have a large number of 

 intermediate forms which, in my opinion, bridge over the apparent 

 gap between the ends of the series. 



The chief differences between such specimens as PI. VI. Fig. 1 

 and the forms of Ruffordia Gopperti previously described, consist 

 in the greater breadth of the ultimate segments and the more open 

 character of the pinnae. The venation of the pinnules is very 

 distinctly shown in the figured specimen, PL VI. Fig. la ; the veins 

 are flabellately disposed and repeatedly forked ; the margin of the 

 pinnules are, for the most part, distinctly dentate. Cf. Fontaine's 

 figure of S. acrodentata, pi. xxxiv. figs. 4 and 4a ; also Mantell's 

 figure of S. Phillipsii? 



On the same piece of ironstone, associated with the sterile 

 portions of a frond, occur fragments of small fertile fronds ; also 

 several pieces of fronds with the rachis tripinnately branched and 

 showing very little leaf lamina, the serrate divisions of the ultimate 

 branches recalling, to some extent, Onychiopsis Mantelli (Brong.). 

 Possibly these different fragments belong to the same plant, but of 

 this there is no real evidence. Ecclesbourne. Rufford Coll. 



V. 2355. The rachis and venation of the pinnules distinctly 

 shown. Very similar to V. 2333, but the segments somewhat 

 narrower. Ecclesbourne. Rufford Coll. 



V. 2158, V. 2327, V. 2357, V. 23570. These specimens are 

 regarded as fragments of the same variety. Ecclesbourne. 



Rufford Coll 



1 Potomac Flora, p. 90, pi. xxxiv. fig. 4. 



2 Geol. S.E. England, p. 239, fig. 2. 



