24 EamSETITES. 



So far as facts are available, we are warranted in the conclusion 

 that the species of the genus Equisetum, from the Upper Carboni- 

 ferous period to the present day, appear to have undergone but 

 little change in habit and external appearance ; the most striking 

 difference being one of size. In the Triassic period, when 

 Hquisetites seems to have reached its maximum development, we 

 find an abundance of very large stems ; from that time the size 

 gradually decreases, and, in the Wealden strata, the few species 

 that are known approach much more nearly in size to the living 

 members of the family. 



1. — Equisetites Lyelli, Mantell. 



1833. Equisetim Lyelli, Mantell, Geol. S.E. England, p. 245, figs. 1-3. 



1845. Equisetites Lyelli, Unger, Gen. spec, plant, foss. p. 60. 



1848. lEquisetites Lyelli, Bronn, Index Pal. Nomencl. p. 464. 



1849. Equiaetiem Lyelli, Brongniart, Tableau, p. 107. 

 1854. Equisetites Lyelli, Morris, Brit. foss. p. 8. 



1869. Equisetum Lyelli, Schimper, Trait, pal. Teg. vol. i. p. 265, and vol. 



iii. p. 453. 

 1871. Equisetum Lyelli, Schenk, PalseontograpHca, vol. xix. p. 207, pi. xxii. 



figs. 10-13. 

 1882. Equisetites Lyelli, Renault, Corns bot. foss. vol. ii. p. 150. 

 1889. Equisetum Lyelli, Fontaine, Potomac Flora, p. 65, pi. i. fig. 7 ; pi. ii. 



figs. 4 and 5. 



Type. Small pieces of stem of an average thickness of 1-5 cm. ; 

 internodes about 2'5 cm. in length, the leaf-sheaths divided into 

 numerous linear acuminate teeth. The surface of the internodes 

 shows faintly marked and numerous longitudinal lines. Single 

 branches at the nodes of frequent occurrence. Sporangia and 

 spores unknown. 



The majority of the specimens in the British Museum are pieces 

 of stems showing the leaf-teeth projecting some distance above 

 each node, and also in a few instances there is a thin brown film 

 on the surface of the internodes. This brown surface layer is 

 all that remains of the plant tissues, and probably is simply the 

 remains of the epidermal layer of cells; it is weU shown in 

 specimens V. 59 and V. 2864. 



