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.
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.
Fig. 280. Onychiopsis Mantelli. (From Wealden specimens in the British Museum; No. 13495 and No. V. 2615. A, natural size; B, very slightly enlarged.)