The fertile segments (fig. 278, D) bear so close a resemblance to those of species of _Onychium_ that it would seem justifiable to regard the plant as a member of the Polypodiaceae. This fern is one of the most characteristic members of the Wealden floras; it occurs in abundance in the English Wealden, in Portugal, Germany, Belgium, Japan, Bohemia, South Africa, and elsewhere. A piece of rhizome figured from the English Wealden[940] is very similar to the creeping rhizomes of recent species of Polypodiaceae. The English Wealden specimens shown in fig. 280, A and B, illustrate the difference in form presented by leaves of this species; the smaller pinnae reproduced in fig. A are more characteristic of the species than are those of the slightly enlarged example represented in fig. 280, B. [Illustration: FIG. 280. _Onychiopsis Mantelli._ (From Wealden specimens in the British Museum; No. 13495 and No. V. 2615. A, natural size; B, very slightly enlarged.)] Among British Tertiary species referred to Polypodiaceae, it is interesting to find what may well be an authentic record of a fern closely allied to the recent tropical species _Acrostichum_ (_Chrysodium_) _aureum_. This Eocene species from Bournemouth is described as _Chrysodium lanzaeanum_[941]. The frond is simply pinnate and apparently coriaceous in texture, with lanceolate or oblong lanceolate pinnules (fig. 261, A, A′, p. 350), differing from those of _Acrostichum aureum_ in being sessile. A prominent 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_[942] 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[943] from Tertiary beds of Montana. A species described by Saporta[944] from the Eocene of Sézanne 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[945].” =Dipteridinae.= _Dictyophyllum._