6 BRITISH FERNS. 



Cryptogramma (Hooker).— Apparently identical with Allosorus. Exotic 

 species few in number. 



PoLYPODiUM (Smith).— Margin of the frond flattened, not concealing the 

 masses of thecse. British species, 1. Vulgare ; 2. Phegopteris ; 

 3. Dryopteris. Exotic species, very numerous. 



WooDSiA (Smith).— ThecEe intermixed with bristles supposed to be ana- 

 logous to an indusium. British species, 1. Ilvensis. Exotic 

 species few in number. 



Acrostichum (Bolton).— Veins forming a complex network, whereas, in the 

 preceding genera, they are never united or connected after 

 leaving the midvein. Exotic species, l.Reticulatum ; 2. Obliquum; 

 3. Crassifolium, and four others. (Family doubtful.) 



Family 111.— Aspidiace^.— Thecse in a circular mass, covered by an indusium. 



Cystopteris. — Indusium annexed to the frond at the insertion of the 

 thecffi, which it contains as in a cup ; the unattached margin of 

 the cup is striated and ragged. British species, 1. Fragilis. 

 Exotic species numerous. 



Cistopteris (Hooker) . a 



Cystea (Smith) i Are identical with Cystopteris. 



Cyclopteris (Gray) ) 



Aspidium (Smith). — Indusium attached by the centre only ; lateral veins 

 anastomozing, and sometimes forming a complete network. 

 Exotic species, 1. Trifoliatum ; 2. Macrophyllum ; 3. Heraclei- 

 folium, and eleven others. 



PoLYSTicHUM. — Indusium attached by the centre only ; lateral veins never 

 united after leaving the midvein. British species, 1. Aculeatum; 



2. LONCHITIS. 



Nephrodiurn (Don). — Indusium reniforra; some, or all of the lateral veins 

 of each pinnula united to corresponding veins in the adjoining 

 pinnula. Exotic species, 1. Molle ; 2. Unitum ; 3. Arbuscula ; 

 and about seventeen others. 



Lastr^a. — Indusium reniform ; veins never uniting after leaving the mid- 

 vein. British species, I. Thelypteris ; 2. Oreopteris, (I 

 expect that these two species will be separated as proposed by 

 Schott, under the names Thelypteris Palustris, and T. Oreopteris ; 

 they differ from the following in bearing the masses of thecae on 

 both branches of the lateral veins when they are forked, whereas 

 the remaining species bear thecae on the anterior branch only ;) 



3. Filix-mas ; 4. Cristata ; 5. Rigida ; 6. Dilatata. Exotic 

 species very numerous. 



Family IV. — Aspleniacece. — Thecae in an elongate mass, covered by an indusium. 



Athyrium (Gray). — Thecae in elongate-reniform, or sausage-shaped 

 masses. British species, 1. Filix-femina. Exotic species 

 few in number, mostly included in the genus Allantodia, which is 

 apparently identical with Athyrium. 



