CH. XXV] COENOPTERIDEAE 433 



rideae as comprising " altogether extinct and generalised " 

 types ^. For these generalised Palaeozoic ferns I propose to use 

 the name Coenopterideae^. This term may be adopted in a 

 wider sense than Renault's name Botryopterideae. The name 

 Primofilices proposed by Arber' might be employed, but the 

 implication which it carries is an argument against its 

 adoption. We have not yet reached a stage in the investi- 

 gation of extinct types at which we are able to recognise 

 what are actually primary or primitive ferns. The search for 

 origins will continue; as new discoveries are made our point 

 of view shifts and the primitive type of to-day may to-morrow 

 have to take a higher place. The epithet primitive or primary 

 is in reality provisional : to adopt such a name as Primo- 

 filices suggests a finality which has not been, or is likely to 

 be, achieved. The true ancestral type — the Urform — which 

 we strive to discover eludes the pursuer like a will-o'-the-wisp. 

 Seeing that the number of true ferns of Palaeozoic age has 

 been recently considerably reduced and is likely to suffer further 

 reduction, the consideration of such undoubted Carboniferous 

 and Permian examples of the Filicales as are left acquires a 

 special importance. In the first place it is natural to ask 

 whether the Palaeozoic ferns include any types which, if not 

 themselves ancestral forms, may serve to indicate the probable 

 lines of evolution of existing families. It is probable that in 

 the near future our knowledge of the Coenopterideae will be 

 considerably extended; as yet we possess meagre information 

 in regard to those characters on which most stress has generally 

 been laid in the classification of recent ferns, namely the 

 structure of the spore-bearing organs. The sporangia of 

 Diplolabis and Stauropteris (figs. 309, A ; 322) are exannulate ; 

 in the former genus they occur in sori or synangia consisting 

 of a small number of sporangia, while in the latter they are 

 borne singly at the tips of ultimate ramifications of a highly 



1 Williamson (SS^) A, p. 478. 



^ Koi)'6s = Lat. communis, common or general. I am indebted to my friend 

 Mr L. H. G. Greenwood, Fellow of Emmanuel College, for supplying me with 

 a name to express the idea of the generalized nature of these Palaeozoic ferns. 



3 Arber (06). 



