The fossil genera have been established by M. Ad. Brongniart, from the form of the leaves and the characters of their venation; that is, the distribution of the vessels. In the following descriptions some botanical phrases are necessarily employed; a few terms of frequent occurrence are explained in [Lign. 16].
Pachypteris[81] (thick-fern). [Lign. 17.]—In this genus from the lower Oolite, the fronds are pinnated, or bipinnated, the leaflets entire, without visible veins, having but a single midrib, and contracted at the base. The absence of veins, and the leaflets not being lobed, are the essential generic distinctions.
[81] The names of the genera are derived from pteris, fern, to which prefixed a term indicative of the peculiar characters.
Lign. 17. Pachypteris lanceolata.
Inferior Oolite. Whitby.
Lign. 18. Sphenopteris elegans
Coal-shale, Waldenburg, Silesia.