CHARACTERS OF TRIBES AND GENERA, 999 
late with the rachis. Veins radiating, forked, costa ex- 
centric; venules direct free, their apices clavate, the 
anterior one sporangiferous. Receptacles oblong. Sort 
terminal, elliptical, sub-marginal. Indusiwm oblong, 
attached longitudinally, 
Type, Aspidium truncatulum, Sw. 
Ilust. Hook. and Bauer. Gen. Fil., t. 8; Moore Ind. 
Fil, p. 48 A; J. Sm. Ferns Brit. and For. fig. CAE 
Hook. Syn. Fil., t. 4, fig. 41. 
Oss.—The habit and general appearance of the Fern 
forming this genus is so peculiar and unique that it is diffi- 
cult to point out its place in any natural sequence. Its 
texture, its articulated pinnules, and its terminal sori, indi- 
cate some connection with Nephrolepis, with which it also 
agrees in the apices of the veins being marked by white 
dots, which form a conspicuous row on the superior side of 
the pinnules. S 
In my observation on this genus in 1841 I have sai 
that “this is the only genus in Aspidew besides Mesochlana 
that has elongated sori,” upon this character Mr. Baker, 
in the “ Synopsis Filicum,” has united Mesochlena with 
Didymochlena, thus making a second species, which he 
names D. polycarpa. In doing this he entirely sets aside. 
natural habit, as well as the position of-the sori, and nature 
of the venation, for in habit Mesochlena scarcely differs. 
from the group to which Nephrodium molle belongs, with 
which it agrees in the lower pair of venules anastomosing, 
and the sori being medial on the venules, and which is 
entirely at variance with the character of Didymochlena. 
Upon the same principle the simple fronded Fern Fadyenia 
prolifera is referable to Didymochlena. / 
Sp. D. lunulata (Desv.) (v v.), Hook. Sp. Fi, Hook, . 
Gard, Ferns., pl. 17. 
