FILICINZE. 35 
V. 23652. Two long and narrow tubers joined together. Of. 
Dunker, Wealdenbildung, pl. vii. fig. 3; also Schenk, Paleonto- 
graphica, vol. xxiii. pl. xxvi. fig. 1, and Heer, Fl. Tert. Helvet. 
vol. ii. pl. exly. Eeclesbourne. Rufford Coll. 
V. 2700. Very thin stem, 1 mm. broad and 8 em. long; matrix 
3) 
penetrated by roots. Ecclesbourne. Rufford Coll. 
V. 2833 and V. 2834. Several tubers of the characteristic shape. 
Eeclesbourne. Rufford Coll. 
Class FILICIN &. 
Leaves large in proportion to the stem. Sporangia usually occur 
on the margins or lower surface of ordinary leaves; occasionally 
the fertile leaves are distinguished from the sterile by well- 
marked characters. 
Sub-Class FILICES. 
Isosporous plants. The prothallus (gametophyte generation) 
usually moncecious, of moderately large size, and capable of an 
independent existence. The sporangia usually occur in definite 
groups or sori, with or without indusia. 
INTRODUCTION TO FILICES. 
Probably no fossil plants are more widely known than the 
fragments of fern fronds so abundant in the beds of shale asso- 
ciated with our Coal-Measures. 
When we come to inquire how far paleobotany has made us 
intimately acquainted with the general morphology, the minute 
histology, and the natural affinities of the Coal-Measure ferns, 
it must be admitted that our scientific knowledge of them is 
extremely limited. There are certain forms of Paleozoic ferns, 
and in the Mesozoic floras there are also a few genera, of which 
it is possible to speak with confidence as to family, and occasionally 
as to internal structure; but such cases are exceptional. The 
old generic names such as Pecopteris, Sphenopteris, Neuropteris, 
and others, were instituted as convenient terms by which to 
