PALEOBOTAN Y BERRY. 



347 



abundant representation. In the present abridged account a mere 

 mention of the more important genera that have been recognized 

 must suffice. Associated with these frond genera at many localities, 

 particularly in India, England, and southern Mexico, are the objects 

 commonly referred to the genus Williamson ia. 



Fig. 18.— Types of Williamsoniales. 

 la, b. Williamsonia virginiensis Fontaine from the lower Cretaceous of Virginia (after Fontaine). 



2. Williamsonia spectabilis. Restoration after Thomas, Jurassic of England. 



3. Restoration of Williamsonia mexicana from the Liassic of Mexico (after Wieland). 



4. Frond of Zamites gigas from the Jurassic of England (after Seward). 



5a. Williamsonia whitbiensismicrosporangiate disk from Jurassic of England (after Nathorst). 



5b. Sporophyll of same showing insertion of synangia. 



6a. Bucklandia milleriana from the Jurassic of Scotland (after Carruthers). 



6b. Bucklandia (Yatesia) joassiana from the Jurassic of Scotland (after Carruthers). 



6c. Williamsonia sp. from the Liassic of Mexico (afler Wieland). 



The most celebrated of these is perhaps Williamsonia gigas, dis- 

 covered early in the last century in the Jurassic outcrops along the 

 Yorkshire coast, and the basis for Williamson's historic restoration. 

 These have been found in organic union with foliage and stems. 

 The stems (Bucklandia) were slender, 5 centimeters in diameter, 

 covered with rhomboidal leaf scars, with a crown of Zamia-like fronds 



