FLORAS OF SECONDARY AND TERTIARY PERIODS. 497 



natives of warm countries, occurring in South America, the 

 West Indies, Japan, Australia, Southern Asia, and South 

 Africa. As has been already remarked, the occurrence of 

 genuine Cycads in the Carboniferous vegetation has not been 

 demonstrated, and the same holds good of all the Palaeozoic 

 floras. True Cycads, therefore, so far as known, make their 

 first appearance in the Trias, at the commencement of the Me- 

 sozoic period, where they are represented by the genera Ptero- 

 phyllum, Zamites, and Podozamites. Cycads continue to be 

 abundantly represented throughout the whole Mesozoic series; 

 but they have only been detected by a single dubious example 

 in strata of Tertiary age. The name " Age of Cycads," as 

 applied to the Secondary epoch, is, therefore, from a botanical 

 point of view, an exceedingly appropriate one. 



Besides Cycads, the Triassic Rocks have yielded the re- 

 mains of Ferns, Equisetites, Calamites, and Conifers. The 

 Ferns belong mostly to the genera 

 Neuropteris, Pecofiteris, Acrostichites, 

 Crematopteris, Cydopteris, and Ano- 

 mopteris. A characteristic species of 

 the first of these is figured below 

 (fig. 393). The Conifers of the Trias, 

 lastly, are abundant, the most char- 

 acteristic genus being Voltzia. This 

 genus is related to the existing Cy- 

 presses, and many species of it are 

 found in the Triassic Rocks. 



Fig- 393- Neuropteris elegans. Trias. 



JURASSIC PLANTS. Taken as a whole, the Jurassic period 

 is characterised by the prevalence of Ferns, Cycads, and 

 Conifers ; no Palms or Angiospermous Exogens having been 

 as yet shown to occur. 



The Cycads are extremely abundant, and belong chiefly to 

 the genera Pterophyllum, Otozamites, Zamites, Bucklandia, Cros- 

 sozamia, Williamsonia, Mantellia, &c. The " dirt-bed," as it 



2 I 



