It is by no means easy in dealing with fossil ferns to distinguish between certain Polypodiaceae - such as species of Davallia - and members of the Cyatheaceae.
It is a striking fact that among the numerous Mesozoic Ferns there are comparatively few that can with good reason be referred to the Polypodiaceae, a family which plays so dominant a role at the present day.
6), recorded from several European localities, as well as from North America, Japan, China, Australia, India and Persia, affords an instance of a common type of bipinnate frond similar to Todites Williamsoni, which has been included in the Polypodiaceae; but such meagre evidence of the soral characters as we possess also points to a comparison with the recent fern Todea barbara.
The prothallus and sexual organs may resemble those of the Polypodiaceae; in Aneimia and Mohria the prothallus, though flattened, is not bilaterally symmetrical, the growing point being on one side; a filamentous type of prothallus is known in Schizaea.
The prothalli, while resembling those of the Polypodiaceae, have points of similarity with those of the preceding groups.