The pinna shown in [fig. 271] is the type-specimen of Sphenopteris arguta Lind. and Hutt. from the Yorkshire Inferior Oolite and is indistinguishable from the English examples on which Brongniart founded his species S. hymenophylloides. Fig. 272 shows a specimen from the York Museum illustrating the difference between the sterile and fertile pinnae. The resemblance of some fertile pinnae of Coniopteris hymenophylloides to those of Thyrsopteris elegans has led to a frequent use, without any solid justification, of the generic name of the Juan Fernandez fern for Jurassic and Wealden plants. It is not impossible that some of the fossils described by Heer from Jurassic rocks of Siberia[905] as species of Thyrsopteris are Cyatheaceous ferns, but it is impossible to say with certainty that they are generically identical with the recent species. In his monograph of the Potomac flora of Virginia[906] and Maryland, Fontaine has described as species of Thyrsopteris several specimens of fronds which afford no evidence as to the nature of the sori or sporangia. Some of the fronds referred by this author to Thyrsopteris rarinervis[907], which I examined in the Washington Museum, are in all probability examples of Onychiopsis, a genus included in the Polypodiaceae. The fragments described by Lester Ward[908] as species of Thyrsopteris from the Lower Cretaceous of the Black Hills of North America afford no satisfactory evidence of relationship to the recent type. Similarly Velenovský has described a Lower Cretaceous Onychiopsis from Bohemia[909] as a species of Thyrsopteris, although the fertile segments bear little or no resemblance to those of the Cyatheaceous genus. Some fertile portions of fronds described by Heer[910] as Asplenium Johnstrupi and afterwards as Dicksonia Johnstrupi[911] from the Cretaceous beds (Kome series) of Greenland are very similar to Coniopteris hymenophylloides.
Fig. 272. Coniopteris hymenophylloides. Specimen from the Inferior Oolite, Scarborough; in the York Museum. [M.S.]
Coniopteris quinqueloba (Phillips). Fig. 273.
This species, originally described by Phillips[912] as Sphenopteris quinqueloba, is very similar in habit to C. hymenophylloides, differing chiefly in the smaller size of the leaf and in the narrower ultimate segments. The specimen shown in [fig. 273], B, illustrates the form of the sorus and sporangia.
Fig. 273. Coniopteris quinqueloba (Phillips). A, × 2; B, considerably enlarged. From drawings supplied by Dr Nathorst.
Coniopteris arguta (Lind. and Hutt.[913]). Figs. 274, [275], A.
The sterile pinnae of this species bear pinnules of a type met with in various species of ferns from different horizons; the smaller ones are entire and slightly falcate, while on the lower part of a frond the ultimate segments are longer and have a crenulate margin. The fertile pinnae bear pinnules reduced to a midrib with a narrow border, and terminating in a cup-like indusium ([fig. 275], A). In habit the sterile leaf ([fig. 274]) of this species is similar to the Jurassic Schizaeaceous fern Klukia exilis.