CHARACTERS OF ‘TRIBES AND GENERA. 327 
186.—Arnyrium, Roth. (1788). 
Allantodia sp., R. Br., 1810; Asplenium sp. auct., sect. Athy- 
rium, Hook. Sp. Fil., J. Sm. Ferns Brit. and For. 
Vernation fasciculate, erect or decumbent, solitary or 
becoming cæspitose. Fronds bi-tripinnatifid, 1 to 4 feet 
high, ultimate segments dentate, or deeply laciniated. Veins 
forked ; venules free.  Sporangia unilateral, or often bi- 
lateral on the lower exterior venule. Indusium generally 
vaulted, single or binate, or oblong reniforme, forming 
linear, straight, or curved, generally unequal-sided sori. 
Type. Asplenium Filiz-fomina, Bernh. 
Illust. Hook. and Bauer. Gen. Fil, t. 16; Moore Ind. 
Fil., p. 37, A.; Hook. Syn. Fil., t. 4, fig. 38, E. 
Ons.—The form of the sori in the species included in this 
. genus is very variable, some being unilateral as in Asple- - 
nium, others binate as in Diplazium, while in others the 
indusium is oblong reniform as in Fadyenia, bus the lobes 
are generally unequal, such differences being in many : 
instances found in the same frond, In many the indusium 
_ is cylindrical and vaulted like that of true Allantodia. 
Inthe “Species Filicum,” as well as in “Ferns, British 
and Foreign,” Athyrium is ranked as a section of Asplenium, 
but, for the sake of a more natural grouping of species, I 
deem it best to allow it to rank as a genus; more distin- 
 guished by its habit of growth and the soft and brittle 
“nature, and highly compound character of the fronds, than 
by the character of the sori; and the species may be viewed 
as having more relationship with the compound-fronded | 
Species of Diplazium than with Asplenium. 
. In the “Species Filicum” twenty-nine species are enu- 
merated, but in the “Synopsis” the number is reduced to 
nineteen, ten of which have come under my observation in — 
