560 Notices of Memoirs — 



existing species. The abundance of fossil Ginkgoales in other parts 

 of the world — in Australia, South Africa, South America, China,. 

 Japan, North America, Greenland, Franz Josef's Land, Siberia, and 

 throughout Europe — demonstrates the former vigour of this class of 

 plants, of which but one member survives. This type of Gymnosperm 

 is distinctly foreshadowed in the Palaeozoic vegetation, and as 

 recently as the Eocene period a species of Ginkgo, indistinguishable 

 in the form of its leaves from the living Maidenhair-tree, flourished 

 in Western Scotland. 



D. Ferns. — Although many of the Mesozoic ferns are preserved 

 only in the form of sterile fronds and are of little botanical interest, 

 several examples of fertile leaves are known which it is possible to 

 compare with modern types. The Poly pod iacese, representing the 

 dominant family of recent ferns, are met with in nearly all parts of 

 the world and possess the attributes of a group of plants at the 

 zenith of its prosperity. We may confidently state that so far as the 

 somewhat meagre evidence allows us to form an opinion, this family 

 occupied a subordinate position in the composition of Mesozoic floras. 

 Polypodiaceous sporangia have been met with in Paleeozoic rocks, 

 and their existence during the Mesozoic period is not merely 

 a justifiable assumption, but is demonstrated by the occurrence of 

 undoubted species of Polypodiacese. It seems clear, however, that 

 this family did not attain to a position of importance until the 

 Mesozoic vegetation gave place to that which characterises the present 

 period. The Osmundaceas are now represented by five species 

 of Todea and four of Osmimda. They flourished over the greater 

 part of Europe during the Ehsetic and Jurassic periods ; their 

 remains have been recorded from England, Germany, Scandinavia, 

 Eussia, Poland, Siberia, and Greenland, also from North America, 

 Persia, and China. 



Similarly, the Schiz^acefe were among the more abundant ferns in 

 the Jurassic vegetation. The Cyatheaceas, a family that is now for 

 the most part confined to the tropics, constituted another vigorous 

 and widely spread section in the Jurassic period ; we find them in 

 Jurassic rocks of Victoria, as well as in several regions in Europe, 

 North America, and the Arctic regions. 



The fertile fronds of many of the fossil Cyatheaceas bear a striking, 

 resemblance to that isolated survivor of the family in Juau 

 Fernandez — Thyrsopteris elegans. It is true that a considerable 

 number of ferns of Jurassic and Wealden age have been described 

 by the generic name Thyrsopteris without any adequate reason ; but, 

 neglecting all doubtful forms, there remain several types represented 

 in the Jurassic flora of Siberia, England, and other parts of the 

 world, which enable us to refer them with confidence to the 

 Cyatheacese and to compare them more particularly with the sole 

 existing species of Thyrsopteris. The GleicheniaceEe, at present 

 characteristic of tropical and southern countries, were undoubtedly 

 abundant in the northern hemisphere in early Cretaceous days ;. 

 abundant traces of this family are recorded from Greenland as well 

 as from more southern European latitudes. 



