- A. Palmatopteris.
- B. Mariopteris. (A, B, after Potonié.)
- C. Diplotmema Zeilleri, Stur. (After Zeiller.)
- C′. D. Zeilleri. Pinnule. (× 3. After Zeiller.)
- D. Neuropteris macrophylla. (British Museum.)
- D′. N. macrophylla. Pinnule. (Slightly enlarged. After Kidston.)
- E. N. heterophylla. Pinnule. (Slightly enlarged. After Zeiller.)
- F. N. Scheuchzeri. (Slightly reduced. After Kidston.)
- G. Alloiopteris Essinghii. (Enlarged. After Potonié.)
Diplotmema.
This generic name is employed by Zeiller[1424] and other authors in a more restricted sense than that in which it was originally used by Stur. The Upper Carboniferous species Sphenopteris furcata Brongn. ([fig. 352], E) may serve as the type. This species occurs in the Middle and Lower Coal-Measures of Britain[1425]. The main rachis gives off branches as in Mariopteris, but in Diplotmema each naked lateral branch is forked at its apex into two opposite pinnae bearing deeply dissected Sphenopteroid pinnules. Zeiller[1426] and Stur have recorded fertile specimens of Diplotmema, but in no case have actual sporangia been discovered. In the species Diplotmema Zeilleri Stur ([fig. 354], C, C′) two Aphlebiae occur at the base of each secondary axis[1427]. It has been pointed out by Potonié that in Diplotmema furcatum the equal dichotomy of the lateral branches is not characteristic of the frond as a whole. In the case of branches higher on the rachis the dichotomy becomes unequal and the forked axis is gradually replaced by a simple pinna ([fig. 354], A). For this type of frond, Potonié proposed the generic name Palmatopteris in place of Diplotmema, which he discards. The long comparatively slender rachis of P. furcata suggests comparison with the liane species of Lygodium[1428].
Fig. 355.
- Cephalotheca mirabilis, Nath. Fertile pinnae. (Partially restored. After Nathorst.)
- C. mirabilis. Sterile pinnule. Nat. size. (After Nathorst.)
Cephalotheca.
This genus was proposed by Nathorst[1429] for some peculiar bipinnate fertile fronds from the Upper Devonian rocks of Bear Island. The pinnae bear slender forked ultimate segments represented by a few detached fragments ([fig. 355], B), associated with the rachises. The fertile pinnae are given off in opposite pairs from the main axis over which they are concrescent ([fig. 355], A). A mop-like cluster of sporangia is borne on the lower surface and close to the base of a fertile pinna: the exannulate sporangia are compared with those of Scolecopteris. Nathorst compares Cephalotheca with a Belgian species of Upper Devonian age described by Crépin[1430] as Rhacophyton condrusorum and by Gilkinet[1431] as Sphenopteris condrusorum. A similar fossil is also described by Baily[1432] as Filicites lineatus from the Kitorkan Grits of Ireland.
The position of Cephalotheca cannot be definitely determined from the available data, but it is more probable that it was a seed-bearing Pteridosperm and not a true fern. Zeiller[1433] has recently expressed the same opinion.