GENERA OF FERNS. 419 
An arrangement and definition of the Genera of Ferns, with 
observations on the affinities of each genus. By J. Smitu, 
.L.S. 
(Continued from page 198, of the preceding volume). 
Tribe VI. DicksoNrEz, J. Sm. 
Sort marginal, round, globose, vertically oblong, or trans- 
versely elongated, furnished with a special interior attached 
lateral indusium, which connives more or less with the 
changed indusiiform margin of the frond, and forms with it 
an urceolate, calyciform, or bilabiate cyst, or marginal groove, 
containing the sporangia. 
Obs. The general feature of this tribe is exhibited by the 
genera Lindsea, Davallia, and Dicksonia, as also Tricho- 
manes, and Hymenophyllum, as characterized by Swartz, Will- 
denow, and others, and which may be viewed as a tribe form- 
ed by a combination of the characters of Aspidiee, and 
Pteridee ; the special interior attached indusium being ana. 
logous to the lateral indusia of many Aspidiew, and the 
changed or indusiiform margin being analogous to the exterior 
attached indusium of Pteridee, or even more analogous to 
those genera of Polypodiee, in which the margin is revolute 
and indusiiform : these tribes have more or less affinity with 
each other in the habit and character of some of their genera. 
The principal distinction between Aspidiee and the present 
tribe is in the sori of Dicksoniee being seated under or on 
the immediate margin, or projecting beyond the margin in 
the form of fertile crenules; but exceptions to the strictness 
of this character are exhibited in some species of the genera 
Humata and Leucostegia, the sori of which are slightly in- 
tramarginal with a simple reniform or vertically oblong in- 
dusium, the marginal or accessory indusium being scarcely 
manifest ; therefore, in such cases, it becomes difficult to 
Characterize them from Nephrolepis, and some species of 
Lastrea, while their habit indicates them as having more 
