156 FILICES. 



Cyatheaceae, are with him founded chiefly on the analogies which seem to 

 exist between his genera and a fossil form hitherto of very doubtful nature, 

 which Corda 1 described as Chorionopteris gleichenioides, and without 

 any apparent reason referred to Gleicheniaceae. This object is a diminutive 

 fragment of a fruiting fern-leaf from the Coal-measures of Radnitz in 

 Bohemia ; it is found in the silicified beds of Millstone grit in that 

 locality, and shows the structure when the sections are examined in direct 

 light. A thin axis bears several closed capsules about a millimetre in 

 diameter, which are formed of several layers of cells and are of a solid 

 character. Each capsule opens by four valves and contains four sporangia 

 filled with spores. There is no indication of an annulus on the thin wall of 

 the sporangia, and their points of attachment are not clearly shown. If we 

 adopt Stur's very natural comparison of this many-lobed indusial capsule 

 with that of Calymmotheca, yet the structure of the sporangia would 

 scarcely suggest any close affinity with Cyatheaceae. 



Stur founded his genus Diplotmema, as has been already shown, 

 merely on the form and mode of branching of the lamina of the leaf, and 

 compared it with the recent genus Rhipidopteris. Points of attachment of 

 the fructifications are of rare occurrence on the leaves, and in Diplotmema 

 Zwickauiense, Gutb., the one species in which they appear, they are found 

 on the terminations of the tertiary nerves, which emerging from the surface 

 of the leaf within the margin form in a peculiar way a small disk-like and 

 toothed expansion. On this structure the unknown sporangia are supposed 

 by Stur to have been seated, which is possible but is certainly not proved 2 . 

 The same author 3 had previously given a different description of the 

 fructification of D. geniculatum, and placed it in the bifurcation of the leaf- 

 stalk, where he still keeps it. With other authors, Zeiller for example, I am 

 disposed to see in these objects simply buds, such as those which shoot 

 forth so abundantly in the forks of the leaves of Gleicheniaceae. 



A number of fossil remains have been directly united with the recent 

 monotypic genus Thyrsopteris, Kze, which lives in the Island of Juan 

 Fernandez and was placed by Mettenius with Cyatheaceae, solely on 

 account of their appearance and of the character of the receptacles which 

 contain the fructifications, the sporangia being unknown. Heer 4 , relying on 

 several fossil forms from the Oolitic strata of Siberia, is especially earnest in 

 his support of this classification. His descriptions apply most exactly to 

 Thyrsopteris Murrayana, whose fertile pinnate leaves have no lamina, and 

 are covered with stalked cup-shaped involucres concealing the sori. Th. 

 Maakiana is a similar form ; a fossil known as Th. gracilis, Heer, seems to 

 me very doubtful. Th. Murrayana is also found in the Oolitic beds of 



1 Corda (1), t. 54, ff. 7-9. * Stur (3), p. 293, and 4 . 3 Stur (5,. ' Heer (5), 



vol. 4 II, tt. I, 2. 



