605 



daceae. Plants of this natural family, in the form ofZamites (fig. 816), 

 Mantellia (fig 814), Cycadites, and Pterophyllum (fig. 815), may be said 



to characterize the fossil flora of the older oohte beds. These plants 

 take the place of the Lepidodendrons and Sigillarias of the car- 

 boniferous period. The stems are found without any leaves attached, 

 but some suppose that the fronds called Otopteris, are the leaves of 

 some of the species. The occurrence of these tropical forms seems to 

 indicate a warmer climate than now exists in Britain. There are 6 

 existing genera of Cycadacese (^ 1047). Two of these are represented 

 in figs. 817, 818, showing the forms of the stems and leaves or fronds. 



Fig. 813. The Dirt-bed of the island of Portland, containing stumps of fossil Cycadaceae in an 

 erect position. 



Fig. 814. Mantellia nidiformis (Cycadeoidea), one of the silicifled Cycadacea; of the Portland 

 Dirt-bed. 



Fig. 815. Pterophyllum Williamson!, the frond of one of the fossil Cycadacese. 



Fig. 816. Zamites. One of the fossil Cycadaceae. 



