170 Scientific Proceedings, Royal Dublin Society. 



Ginkgo affinibj. There is all over the world a sharp demarcation in the flora 

 and fauna between the Permian epoch, the youngest of the Palseozoic period, 

 and the Triassie, the oldest of the Mesozoic beds. Groups of animals and 

 plants flourishing in the Permian disappear at its termination abruptly as if 

 cut off, to be replaced in the Triassie by other groups usually more highly 

 organized. Does the evidence tend to show that the conditions induced by 

 the Permian " catastrophe " favoured the first uprising and luxuriance in 

 the Mesozoic of the Ginkgoacese ? Their points of agreement with the 

 Cordaitacese, a group of Gymnosperms confined to the Palaeozoic, have 

 suggested that they arose from the Cordaitacese, most abundant in the Upper 

 Carboniferous, and that they replaced this group in part in the Mesozoic. 



Of all the types of foliage hitherto described from the Palaeozoic the one 

 from the Permian rocks of Lodeve, named by Saporta (3), Ginkgoplnjllmn 

 Grasseti, seems to come nearest to Ginkgo itself. In it the leaves are obscurely 

 arranged distichously, and show a long petiole, 2 mm. wide, but with a decurrent 

 base of attachment. The lamina is elongated, cuneiform, and several times 

 bifurcate. Each terminal bilobed portion is truncate, toothed. The veins are 

 shown dichotomously divided, though they are not described in detail. No 

 reproductive organs are known. G. Grasseti comes very near Baiera, to which 

 it is united by Heer, but its decurrent leaf-bases separate it from that genus. 

 Whittleseya is another genus, the affinities of whieli are highly suggestive 

 of Ginkgo. It has been described as the earliest member of the group, 

 and is well represented by several species in the Carboniferous strata of 

 Pennsylvania, &c. 



Further, in the "Fossil Flora of Great Britain," Lindley and Hutton 

 describe and figure a fossil from the Carboniferous strata under the name of 

 Noeggerathia flabeUata (4) which became subsequently the type of the genus 

 Psygmophyllum created by Schimper (5), to include forms characterized by 

 wedge- or fan-shaped leaves, traversed by dichotomously divided veins, 

 passing as a few strands into a leafstalk formed by the gradual tapering of 

 the lamina ; the shape and venation of the leaf being the chief generic 

 characters. 



The earliest recorded specimen of this type is a leaf assigned to the genus 

 by Nathorst (6) under the name o£ Fsygmophyllum Williamsoni, sp, no v. from 

 the Upper Devonian beds of Spitzbergen. P. Williamsoni is regarded by 

 Nathorst as the most important of the remains discovered in the Devonian 

 beds of Spitzbergen. As drawn, it is strikingly like tlie figure in " Fossil 

 Flora" (plate xxix) of N.flabellata. In both, the obcuneiform or obtriangular 

 simple leaf (or leaflet ?) shows a broad apical or distal margin which, as far 

 as traceable, was indented or lobed. The base tapers, so that its shape here 



