66 
HISTORY OF BRITISH FERNS. 
4. L. inundatum, Linnaeus. —Leaves scattered, curved up¬ 
wards, linear; spikes solitary, sessile. Plate XX. fig. 4. 
5. Ii. alpinum, Linnaeus. — Leaves in four rows, of two 
forms, imbricate ; spikes solitary, sessile. 
Genus 21. SELAGINELLA, Spring. 
I S. spinosa, Pal. de Beauvais. —Leaves scattered, half- 
spreading, lanceolate; spikes solitary, sessile. 
III. PEPPER-WORTS, or MARSILEAOEJE. 
Genus 22. ISOETES, Linnaeus. 
1. I. lacustris, Linnaeus. —The only species. Plate XIX. 
fig. L 
Genus 23. PIL U LA RI A, Linnaeus. 
1. P. globulifera, Linnaeus. — The only species. Plate 
XVII. fig. 2. 
IV. HORSETAILS, or EQUISETACEiE. 
Genus 24. EQUISETUM, Linnaeus. 
1. E. Telmateia, Ehrhart. —Stems dissimilar, the sterile 
branched, smooth, with about thirty ridges; sheaths 
