FLORAS OF SECONDARY AND TERTIARY PERIODS. 467 



Fig. 715 —MmitelKa (Cycadeoidea) megalopliylla, 

 a Cj'cad from the Purbeck "dirt-bed." Upper 

 Oolites. 



The Cycads are extremely abundant, and belong chiefly 

 to the genera Pterophylluiii, Otozamites, Zamites, Bucklandia, 

 Crossozamia, Williamsonia, 

 Mantellia, &c. The " dirt- 

 bed," as it is called, of the 

 Purbeck beds, consists of 

 an ancient soil, in which 

 stand erect the trunks of 

 Conifers and the stems of 

 Cycads of the genus Man- 

 tellia (fig. 7 1 5).' The fronds 

 of Cycads occur also in 

 great abundance in various 

 Jurassic strata, especially 



in the lower portion of the series; and the cones likewise have 

 been in some instances preserved. The Conifers are repre- 

 sented by various genera 

 more or less nearly allied 

 to the present Araucarice, 

 and cones have been in a 

 few instances detected. 



Ferns occur very abun- 

 dantly in the Jurassic 

 series, the commonest 

 genera being Coniojpteris 

 (fig. 716), Odontoj^teris (fig. 

 717), Sphenopteris, Cyclop- 

 teris, Phlehopteris, Pecop- 

 teris, Polypodites, Pachyp- 

 teris, and Tmniopteris. 



Endogens are by no 

 means unknown in the 

 Jurassic series, though 

 no representative of the 

 group of the Palms has 

 been as yet detected. 

 Amongst the most im- 

 portant of the Oolitic 



Endogens may be men- rig. tig.— Coniopferis Murmyana. Great Oolite. 



