GENERA OF FERNS. 421 
97. IsoLoMa, J. Sm. 
(Lindseece sp. Wall. Hook. et Grev. Presl. Vittarie? 
Wall. herb.). 
Costa central; veins forked; venules direct, their apices 
transversely combined by a continuous sporangiferous recep- 
tacle; special indusium linear, plane, equal with the indusii- 
form margin ; sporangia vertical. 
Fronds. from l to 2 feet high, linear, pinnate; pinne ob- 
long-elliptical, or lanceolato-falcate, truncate or auriculated . 
at the base; petiole short, articulated with the rachis, smooth 
or pubescent ; veins free in the sterile pinne. 
Species. 1. I. lanuginosum, J. Sm. (Lindsea Wail. Vit- 
taria? Wail). 2. I. divergens, J. Sm. (Lindsea Hook. et 
Grev. Vittaria Wail.) 
lilust. Hook. et Grev. Ic. Fil. t. 226. 
Obs. 'The two known species which I have placed in this 
genus are so similar in habit to several species of Nephro- 
lepis, that in the absence of sori they would readily be 
viewed as belonging to that genus ; but the continuous sorus 
shows their affinity to Lindsea, as hitherto characterized. 
But the peculiar habit of Isoloma is at variance with every 
known species of Lindsea, and is more particularly exem- 
plified in the deciduous nature of the pinnz, the petiole 
being articulated, as in Nephrolepis, Didymochlena, &c. It 
also agrees with these genera by the apex of the sterile 
venules, (which is usually thickened), producing a white 
chalky substance in the form of a dot on the superior side 
near the margin of the frond, forming a conspicuous mar- 
ginal row. These characters are not found in any species of 
Lindsea, as now characterized ; and Isoloma also differs in 
having a true central mid-rib, whack | in Lindsea is eccentric, 
or entirely absent. This very distinct habit has, therefore, 
induced me to separate this genus from Lindsea; and I 
may also mention that the sporules of Lindsea are globose, 
and angular, while in Zsoloma they are elliptical, slightly reni- 
form and smooth, like the sporules of NepArolepis. 
