From Jurassic rocks in various parts of the world numerous fossils have been described under the generic names _Aspidium_, _Asplenium_, _Davallia_, _Polypodium_, and _Pteris_. In the great majority of cases such records leave much to be desired from the point of view of students who appreciate the dangers of relying on external similarity between vegetative organs, and on resemblances founded on obscure impressions of sori. The generic term _Woodwardites_[933], which suggests affinity with the recent genus _Woodwardia_, has been used for Rhaetic plants belonging to the Dipteridinae. A plant described as _Adiantides Lindsayoides_ from Jurassic rocks of Victoria[934], characterised by marginal sori which appear to be protected by the folded-over edge of the leaflets, and by the resemblance of the pinnules to those of recent species of _Lindsaya_, may be a true Polypodiaceous fern; but in this case, as in many similar instances, nothing is known of the structure of the sporangia. Some sterile pinnae described by Yabe from Jurassic rocks of Korea as _Adiantites Sewardi_[935] may perhaps be identical with the Australian species. In such a species as _Polypodium oregonense_ Font., from Jurassic rocks of Oregon, the generic name is chosen because the “fructification seems near enough to that of _Polypodium_ to justify the placing of the plant in that genus[936].” But the fact that no sporangia have been found is a fatal objection to this identification. _Onychiopsis._ This generic name was instituted by Yokoyama[937] for a Japanese Wealden species, previously described by Geyler[938] as _Thyrsopteris elongata_, on the ground that, in addition to a similarity in habit of the sterile fronds, the fertile pinnae present a close agreement to those of the recent genus _Onychium_. _Onychiopsis Mantelli_[939] (Brongn.). Figs. 278, D; 280, A and B. The Japanese species _Onychiopsis elongata_ may perhaps be identical with this common Wealden fern which, as Fontaine points out, should be called _O. psilotoides_ if the rule of priority is to be observed irrespective of long usage. 1824. _Hymenopteris psilotoides_, Stokes and Webb, Trans. Geol. Soc. [ii.], Vol. I. p. 423, Pl. XLVI. fig. 7. 1828. _Sphenopteris Mantelli_, Brongniart, Hist. vég. foss. p. 170, Pl. XLV. figs. 3–7. 1890. _Onychiopsis Mantelli_, Nathorst, Denksch. Wien Akad. Vol. LVII. p. 5. _Onychiopsis Mantelli_ may be defined as follows:— Frond bipinnate, ovate lanceolate, rachis winged; pinnae approximate, given off at an acute angle; pinnules narrow, acuminate, with a single vein; the larger segments serrate and gradually passing into pinnae with narrow ultimate segments. Fertile segments sessile or shortly stalked, linear ovate, sometimes terminating in a short awn-like prolongation.