624 
Notes . 
theory ; on account of them, the Equisetineae are placed in an isolated 
position, and in the same way, though with less pressing grounds, a 
separate position should be accorded to those types which lie between 
the extremes of Ly copods and Ferns, in proportion as the cross- 
characters are more or less pronounced. 
On this basis the Isoetaceae would probably best take their place 
as a sub-series of the Lycopodiales, Ligulatae ; the Psilotaceae and 
Sphenophylleae would constitute a series of Sphenophyllales, separate 
from, but related to, the Lycopodiales. The Ophioglossaceae would 
form an independent series of Ophioglossales, more aloof than the 
Sphenophyllales from the Lycopodiales, but not included in the 
Filicales. The actual connexion of these series by descent must 
remain open ; it is quite possible that some or all of them may have 
originated along distinct lines from a general primitive group, which 
may be provisionally designated the Protopteridophyta ; these were 
probably small-leaved strobiloid forms, with radial type of construction, 
and with the sporangia disposed on some simple plan. The grouping 
arrived at in these Memoirs may be tabulated as follows : — 
PTERIDOPHYTA. 
I. Lycopodiales. 
(a) Eligulatae. 
Lycopodiaceae. 
( b ) Ligulatae. 
Selaginellaceae. 
Lepidodendraceae. 
Sigillariaceae. 
Isoetaceae. 
II. Sphenophyllales. 
Psilotaceae. 
Sphenophyllaceae. 
III. Ophioglossales. 
Ophioglossaceae. 
IV. Filicales. 
(a) Simplices. 
Marattiaceae. 
Osmundaceae. 
F. O. Bower. 
Schizaeaceae. 
Gleicheniaceae. 
Matonineae. 
($) Gradatae. 
Loxsomaceae. 
Hymenophyllaceae. 
Cyatheaceae. 
Dicksonieae. 
Dennstaedtiinae. 
Hydropterideae (?). 
(c) Mixtae. 
Davallieae. 
Lindsayeae. 
Pterideae, and other Poly- 
podiaceae. 
V. Equisetales. 
Equisetaceae. 
Calamarieae. 
