IX] EQUISETITES. 257 



gigantic Equisetums which resembled modern Horse-tails in a 

 remarkable degree. In the succeeding Jurassic period tree-like 

 Equisetums were still in existence, and species of Equisetites 

 are met with in rocks of this age in nearly all parts of the 

 world. A few widely distributed species are known from 

 Wealden rocks, but as we ascend the geologic series from the 

 Jurassic strata, the Equisetums become less numerous and 

 the individual plants gradually assume proportions practically 

 identical with those of existing forms. 



I. Equisetites. 



The generic name Equisetites was proposed by Sternberg 

 in 1838^ as a convenient designation for fossil stems bearing a 

 close resemblance to recent species oi Equisetum. Some authors 

 have preferred to apply the name Equisetum to fossil and recent 

 species alike, but in spite of the apparent identity in the 

 external characters of the fossil stems with those of existing 

 Horse-tails, and a close similarity as regards the cones, there 

 are certain reasons for retaining Sternberg's generic name. It 

 is important to avoid such nomenclature as might appear to 

 express more than the facts admit. If the custom of adding the 

 termination -ites to the root of a recent generic term is generall}' 

 followed, it at once serves to show that the plants so named 

 are fossil and not recent species. Moreover, in the case of 

 fossil Equisetums we know nothing of their internal structure, 

 and our comparisons are limited to external characters. Stems, 

 cones, tubers, and leaves are often very well preserved as sand- 

 stone casts with distinct surface-markings, but we are still in 

 want of petrified specimens. There is indeed evidence that 

 some of the Triassic and Jurassic species of Equisetites, like the 

 older Calamites, possessed the power of secondary growth in 

 thickness, but our deductions are based solely on external 

 characters. 



In the following pages a few of the better known species of 

 Equisetites are briefly described, the examples being chosen 



> Sternberg (38) p. 43. 



