380 FILICALES [CH. 



midrib gives off numerous anastomosing veins. No fertile 

 pinnules have been found. 



Specimens described by Forbes from the Eocene beds of the 

 Island of Mull as Onoclea hebraidica^ bear a strong likeness 

 to the North American and Japanese recent species Onoclea 

 sensibilis. Fertile specimens referred to the latter species are 

 recorded by Knowlton^ from Tertiary beds of Montana. 



A species described by Saporta^ from the Eocene of 

 Sezanne as Adiantum apalophyllum is recorded by Gardner 

 and Ettingshausen from Bournemouth ; an identification which 

 is based on somewhat meagre evidence. 



The following remarks by Gardner and Ettingshausen are 

 worthy of repetition as calling attention to circumstances often 

 overlooked in analyses of fossil floras. They speak of ferns as 

 relatively rare in British Eocene rocks and add, — " the floras 

 consist principally of deciduous dicotyledonous leaves, which... 

 fell into the water and were tranquilly silted over. Ferns, on 

 the other hand, would require some violence to remove them 

 from the place of their growth, and their preservation would 

 consequently be exceptional, and they would be mutilated and 

 fragmentary. This may account for their rarity. Few as the 

 British ferns are in the number of species, they nevertheless 

 form the largest and most important series of Eocene ferns, 

 even of Tertiary ferns, yet described from one group of beds^" 



Dipteridinae. 



Dictyophyllum. 



This genus was founded by Lindley and Hutton for a 

 pinnatifid leaf from the Jurassic rocks of Yorkshire which they 

 regarded as probably dicotyledonous and named D. rugosum^. 

 Several ferns of this genus have since been found with well- 

 preserved sori which demonstrate a close similarity to the recent 

 fern Dipteris. Dictyophyllum may be defined as follows : — 



^ Forbes (51) ; Gardner and Ettingshausen (82). 



2 Knowlton (02) PI. xxvi. 



^ Saporta (68) A. ; Gardner and Ettingshausen (82) PI. x. fig. 1. 



■* Gardner and Ettingshausen (82) p. 21. 



5 Lindley and Hutton (34) A. PI. civ. 



