THE EVIDENCE 79 



frequent, but such evidence is not to be relied on, 

 for in certain cases these leaves have proved to 

 belong to plants widely different from the modern 

 Cycadaceae, though no doubt belonging to the 

 class Cycadophyta. So far as our present knowl- 

 edge goes, the family Cycadacese, though existing 

 in Mesozoic times, seems to have attained no 

 great development. 



The vast majority of the Mesozoic Cycadophyta 

 hitherto investigated have proved to belong to a 

 group resembling the recent Cycads in habit and 

 vegetative structure, but beyond comparison 

 more highly organised as regards the reproductive 

 organs. This is the family of the Bennettitese, 

 which are well represented in Britain, France, 

 Italy, and other parts of Europe, but far more 

 abundantly in the United States, where Mary- 

 land, Dakota and Wyoming are richer in these 

 fossils than any other part of the world. 



In Britain, Cycads of this family have been 

 found in the Lower Greensand and the Wealden 

 of the Isle of Wight, in the Wealden of Sussex, in 

 the Purbeck Beds (Upper Jurassic) of East Dorset- 

 shire, in the Great Oolite of Brora in the north of 

 Scotland, and in the Inferior Oolite of the York- 

 shire coast. The most valuable specimens are 

 those which are petrified, so that the internal 

 structure is preserved; one of the most famous 

 fossils of this kind is Bennettites Gibsonianus, 



