EQUISETITES. 105 
Equisetum Lyreiiu. Lign. 12.— A species which I dis- 
covered in Wealden limestone, at Pounceford (Geol. S. L. 
p- 245), must have closely resembled the Lquisetum fluvi- 
atile: it has an articulated cylindrical stem, and regularly 
dentated sheaths, embracing the stem at the joints. 
A transverse slice of the stem exhibits under the micro- 
scope a cellular structure filled with cale-spar, and forms a 
beautiful object when viewed with the polarizing apparatus. 
Lien. 12. EevutisEtum LYELLit. 
Wealden. Pounceford. nat. 
Fig. 1.—A stem, having two sheaths, and a bud at the lowermost joint. 
2.—Stem of a young plant, with sheaths, preserved in pyrites. 
3.—Stem, with the cryptogamous head or upper end. 
This plant occurs in many localities of the Wealden in 
Sussex and Kent; from the railway cuttings near Tonbridge, 
I collected several fine specimens; it is met with also in the 
cliffs near Hastings. 
HQuiserires cotumnaris. Lign. 13.— A gigantic species 
of Equisetum abounds in the strata of the lower division of 
the Oolitic or Jurassic formation of Yorkshire, and many 
