EOCENE EERNS. 



21 



variation in the form of their fronds, and even in tlie angles and relative proximity of 

 the vennles, errors or nnnecessary multiplication of species have been avoided. Nearly 

 all the specimens from Bournemouth, whence they were chiefly procured, seem to have 

 been macerated so as to discomiect the pinnae and remove the spores. 



Ferns are relatively rare in British Eocenes, and yet some twenty distinct forms are 

 described in this Monograph. The floras consist principally of deciduous dicotyledo- 

 nous leaves, which, in the ordinary course of events, 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 these British forms are in the number of species, they nevertheless form the 

 largest and most important series of Eocene, even of Tertiary Ferns, yet described from 

 any one group of beds. 



Although our knowledge of the Ferns which existed in Tertiary times is still most 

 imperfect, yet we find that nearly all of them have allied living representatives, although 

 none of these now live in the British Isles. So close, in fact, are the resemblances in 

 many cases, that it is difficult to avoid the belief that they are the more or less direct 

 descendants of the fossil forms ; indeed, some Continental authors, think that in the 

 Miocenes of Switzerland the directly intervening forms can be traced. 



A few of the genera here described belong to groups which have not previously 

 been found fossil ; but many of them are Eocene forms already described. It is 

 interesting to find that some of these, like a few living species, ranged synchronously over 

 both hemispheres, as a few are also found fossil in North America. 



One of the most remarkable, and a very abundant form, is a Chri/sodiiiin, which ranges 

 from the Alum-Bay beds at Studland, through the Lower-Bournemouth series, into the 

 overlying marine beds, and has a no less wide range upon the Continent. The 

 Poli/podiece with reticulated venation are represented by at least three species ; numbers of 

 specimens of each having been obtained. Their venation is somewhat abnormal, in one 

 instance approaching so nearly to that of dicotyledons as to leave considerable doubt in 

 my mind as to its determination. The Pleridece arc represented by several species, the 

 most abundant of which is closely allied to many Eocene and Miocene forms already 

 known. Another, of which we have only a fragment, is related to a group with reticu- 

 lated venation now living in Polynesia. A third is hardly distinguishable from the 

 widely distributed Miocene P. (Eningensis. A unique specimen is doubtfully referred to 

 the AsjdenacecB. The Aspidiaceoi have three representatives, one of which possesses 

 a new type of venation, somewhat resembling that of certain dicotyledons, and 

 has been placed by Ettingshausen in a new genus. The others are referred to 

 Phegopteris, and resembles living forms. Gleichenia, well known in Cretaceous times, 

 has only been met with in admittedly Eocene strata at Bournemouth, where it is 

 represented by a trailing or climbing form, of most local and limited distribution. The 



