46 HISTORY OF BRITISH FE11NS. 



1 3 . BlecJmwm = Dorsal-fruited Ferns, having the spore- 



cases in a continuous line between the midrib and 

 margin of the divisions of the frond. 

 E. DICKSONIE^ = Perns whose sori are (in the British 

 species) produced around the ends of veins project- 

 ing from the margin, and surrounded by an urn- 

 shaped or two-valved membrane. It contains the 

 genera Trickomanes and Hymenopkyllum. 



14. Trichomanes = Marginal-fruited Terns, having the 

 sori surrounded by urn-shaped expansions of the 

 frond. 



15. Hymenophyllum = Marginal-fruited Perns, having 

 the sori surrounded by two-valved expansions of 

 the frond. 



ii. OSMUND ACE^E= Perns having the young leaves circinate, 

 the spore-cases destitute of an elastic ring, and burst- 

 ing by two regular valves. It contains the genus 

 Osmunda. 



16. Osmunda = Marginal-fruited Perns, having the 

 regular valved spore-cases in irregular, dense, 

 branching clusters, terminating the fronds. 



iii. OPHIOGLOSSACE.E = Perns having the young leaves folded 

 up straight, the spore-cases destitute of an elastic ring, 



