FILICES. 167 



All the stems hitherto described are marked by the spiral arrangement 

 of the leaves and the numerous orthostichies ; from these the genera Mega- 

 phytum, Artis and Zippe, Corda, which are only known in the form of 

 casts, are most sharply distinguished by the exactly distichous position of 

 their leaf-scars. These genera have no direct analogies in recent vegetation, 

 for all recent fern-stems with distichous arrangement of the leaves are 

 prostrate and creeping, which was certainly not the case with the genera in 

 question, for their structure is radial and exactly the same all round, and 

 there is no indication that one side was turned to the soil and bore roots. 

 The Megaphyta, of which many good figures are to be found in the 

 literature l , appear to have been confined entirely to the Coal-measures ; 

 their huge shield-like leaf-scars are circular in form and in appearance like 

 those of Stemmatopteris. The large bundle-trace has usually the shape of 

 a crescent opening upwards and with its horns bent inwards. There may 

 also be other smaller traces, the character of which has still to be investigated. 

 From the scale of the flattened cylindrical casts, a metre in length, which 

 are met with occasionally, it would appear that these plants must have had 

 tall erect and somewhat slender stems. A magnificent specimen is pre- 

 served in the collection of the Bergschule at Saarbriicken. The genus 

 Zippea 2 , founded on a few remains from the Bohemian Coal-measures, is 

 closely allied to Megaphytum, and the trace has the same character as in 

 that genus, but the leaf-scars are much smaller and less prominent. 



It has been already observed more than once that we are as a rule 

 acquainted only with casts of the fern-stems of which we have hitherto 

 been speaking. The inner structure can only be distinguished in a few 

 cases, but in these it is found not to differ essentially from the ordinary 

 structure of recent stems. This will be seen by examining Renault's 3 

 figure of his Dicksonia Buvignieri, as also the transverse section of Caulop- 

 teris Cottaeana 4 , of which however there is no figure showing the habit ; 

 the drawings also of Pecopteris Cottai 5 may be mentioned in this con- 

 nection. It is uncertain whether this form comes from the Coal-measures 

 or from the Rothliegende, since it has been found in the district of 

 Schwemmland in the neighbourhood of Grossenhain in Saxony. The 

 broad pith of this stem, of which I have seen a transverse section in the 

 Geological Department of the British Museum, is traversed by a rank 

 growth of thin extraneous rootlets which look at first sight like medul- 

 lary bundles. A well-preserved stem of this kind from the Turonian 

 Chalk of Oppeln has been described by Stenzel 6 as Protopteris fibrosa. 

 From the same formation we have the specimen covered with a felt 

 of roots and named by Goppert Rhizopterodendron Oppoliense, which is 



1 Schimper (1), t. 52. 2 Corda (1), t. 26. 3 Renault (2), vol. iii, p. 73, t. 9. 4 Renault 

 2 , vol. iii, t. 8, f. 10. 5 Corda (1), t. 49. * Stenzel (3), t. 3, ff. 30-36. 



