THE FILM FERN. 301 
and one of these, Sphærocionium, distinguished by the capitate termi- 
nation of its receptacles, has met with partial reception as a genus, 
but the character does not appear to be of sufficient importance for 
generic definition; while for sectional subdivisions, such obvious fea- 
tures as those presented by the smooth or serrated margins of the 
fronds are preferable. 
The name is derived from the Greek, hymen, hymenos a film or 
membrane, and phyllon a leaf: thus suggesting the very appropriate 
English name of Film Fern, which is preferable to that of Filmy 
Fern which has been sometimes employed. : 

SYNOPSIS OF THE SPECIES. 
1. H. tunbridgense: pinne subvertical, pinnatifid ; involucres erect, sessile, com- 
pressed, the valves serrate. 
2. H. unilaterale: pinnæ decurved, sub-unilateral, digitately pinnatifid ; involu- 
cres decurved in a direction opposite to the pinnse, stalked, inflated, the 
valves entire. 

