336 CHARACTERS OF TRIBES AND GENERA. 



distinct from Allantodia, especially as the general character 

 of the fronds of Allantodia agrees with Hemidictyum. I 

 nevertheless deem it best to retain it as distinct. 

 Sp. H. marginatum, Presl (v v.). 



194. CETERACH, Willd., in part (1810). 

 Asplenium, sect. Hemidictyum, Hook. Sp. Fil. 



Vernation fasciculate, acaulose, becoming cgespitose. 

 Fronds 2 to 12 inches long, sinuose-pinnatifid, the under 

 side densely squamose. Veins forked ; venules anastomo- 

 sing, obscure. Sporangia unilateral, anterior. Indusium 

 rudimentary. Sori oblong, the sporangia protruding 

 through dense scales. 



Type. Asplenium Ceterach, Linn. 



Illust. Hook, and Bauer Gen. Fil., 1. 113 A. ; Moore Ind. 

 Fil., p. 39 A. ; J. Sm. Ferns, Brit, and For., fig. 117. 



OBS. This genus is founded on a solitary species, which 

 in habit, and the nature of its fructification, is so peculiar 

 that it has given rise to much diversity of opinion as to its 

 proper place in any arrangement, whether natural or arti- 

 ficial. In my " Genera of Ferns " (1841) I stated that its 

 unilateral sporangia indicated it to belong to Asplenece, and 

 that the imperfect or obsolete indusium was owing to the 

 suppression of that organ, caused by the density of the 

 squamae on the under side of the frond. More recent 

 observations have shown the presence of a narrow linear 

 indusium, which is more evident in the large fronded 

 species called 0. aurea, of Madeira, than in the common 

 form. It must, however, be confessed that its peculiarities 

 prevent its association with any species of the asplenoid 

 tribe, except with Asplenium alternans of Wallich, already 

 noticed. In the "Species Filicum" it is placed in the 



