Fig. 268. ? Laccopteris polypodioides. Nat. size. From a specimen in the Whitby Museum (Brit. Mus.).
Laccopteris Dunkeri (Schenk)[878].
This species is represented in several Wealden localities by fragments of fertile pinnae similar to those of L. polypodioides. It is almost impossible to distinguish small specimens of the Wealden fern from Heer’s genus Nathorstia (Marattiaceae) unless the sori are well preserved. This species occurs in Wealden beds in England, Germany, Belgium, and elsewhere and has been discovered by Dr Marcus Gunn in Upper Jurassic plant-beds of Sutherlandshire (N.E. Scotland).
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Laccopteris is widely spread in Rhaetic, Jurassic and Lower Cretaceous floras. It affords evidence of the former abundance in northern latitudes of a family now represented by the two species of Matonia confined to a restricted area in the southern hemisphere.
Matonidium.
Schenk[879] instituted this convenient term for fossil fern fronds agreeing in habit and in their sori with Matonia pectinata (figs. 227, 228, p. 292). Zeiller[880] has drawn attention to the fact that the Mesozoic species differ from the surviving types in the greater number of sporangia in each sorus, and, it may be added, in Matonidium the fertile pinnules are more richly supplied with sori than are those of Matonia. Unfortunately our knowledge of the structure of the sporangia of Matonidium is less complete than in the case of Laccopteris, but such evidence as is available justifies the conclusion that Matonia is a direct descendant of ferns which formed a prominent feature in European Jurassic and Wealden floras. It is interesting to find that in a Cretaceous species, described by Krasser ([fig. 265], A) since the publication of Zeiller’s paper, the sori appear to be identical in distribution and in appearance with those of the recent species.
I am indebted to Prof. Bommer for permission to reproduce the unpublished drawing represented in [fig. 237] D (p. 310) of a section of the rhizome of Matonidium from the Belgian Wealden beds of Hainaut (“Flore Bernissartienne”). The section shows an arrangement of vascular tissue identical with that in the recent species: there may be two solenosteles and in addition a solid axial strand. The form of the leaf-trace in the fossil appears to be identical with that in Matonia pectinata ([fig. 237], A, p. 310).
Matonidium Goepperti (Ettingshausen)[881]. Fig. 269.
Under this name are included specimens from Inferior Oolite and Wealden strata in Britain and elsewhere. It is, however, not impossible that if more information were available, we should find adequate reasons for recognising two specific types. Fontaine[882], adhering rigidly to the rules of priority, speaks of this species as Matonidium Althausii (Dunker), but Ettingshausen’s specific term is better known.