This sub-tribe, instituted by Prantl, has been revived by Bower on the ground that the sori present features intermediate between those of Cyatheaceae and the Polypodiaceous genus _Davallia_. The sporangia have a slightly oblique annulus. =Polypodiaceae.= This section of the Leptosporangiate ferns, including several sub-tribes, comprises the great majority of recent genera. The sporangia form naked or indusiate sori and have a vertical incomplete annulus. In _Plagiogyria_[699] the oblique annulus and soral features suggest comparison with the Cyatheaceae. A more intimate acquaintance with Polypodiaceous ferns will undoubtedly demonstrate the existence of other generalised types[700]. From the point of view of the identification of fossil ferns it is important to bear in mind the very close resemblance presented by some Polypodiaceous species, e.g. species of _Davallia_ (fig. 229, C), to Cyatheaceous ferns (cf. fig. 229, D). =Parkeriaceae.= (_Ceratopteris._) The almost spherical and scattered sporangia are characterised by the peculiar form of the vertical annulus, which is composed of numerous cells differing in their greater breadth and smaller depth from those of a typical annulus. Exannulate sporangia have been described, while others occur showing different stages between a rudimentary and a complete ring. The single species of _Ceratopteris_, _C. thalictroides_, is an annual aquatic fern widely spread in tropical countries[701]. [Illustration: FIG. 231. A, A′. _Dipteris quinquefurcata_ (type-specimen in the Kew Herbarium). B, C, E, G. _D. conjugata._ (C, ⅛ nat. size.) D. _Polypodium quercifolium._ F. _Dipteris Wallichii._ (D, after Luerssen.)] =Dipteridinae.= (_Dipteris._)