CHAEACTBES OF TRIBES AND GENEBA. 337 



sectlou Ileiiiidictyum, along with tlie two species of Asplevi- 

 dictyam and Hemidictyum marginatum, all three very dis- 

 tinct in habit. Although I now place Ceterach after Hemi- 

 dictyurii it is not that I consider it has any relationship, 

 but merely on account of having no ally for it, I place it 

 as an anomalous genus at the end of the tribe. 



Sp. C. officinax'um, Willd. (v v.) {Grammitls, Sw. ; Scolo- 

 pendrium, Sm.). 



Obs. — Found in rocky places, and on old walls in this 

 country, and throughout Europe and the temperate regions 

 of the Northern hemisphere generally. In Madeira the 

 fi'onds attain a large size, and which by some authors has 

 been described as a distinct species under the name of 

 G. auremn. 



B. Ring of Sporangia horizontal, central. 

 Sect. 1. — Sori discal, punctijorm, naked, rarely indnsiate. 



Tribe 24,— GLEICHBNB^. (Plate 24). 

 {Glciclieiiiacece, R. Br.) 



Ods. — This Tribe includes a peculiar group of Ferns, 

 consisting- of about thirty described species, technically 

 distinguished from Folypodiaeece by the sporangia being' 

 surrounded with a horizontal ring' generally at right 

 angles with the axis of attachment. This direction of the 

 ring is common to the whole of true Qlcieheniaceiji, but in 

 Matonia it is partially oblique. 



Independent of the structure of the sporangia, Gleiclie- 

 niacece are readily known from all other Ferns by their 

 fronds being' once or many times dichotomously branched 

 or flabelllform (two species excepted, which have simple 

 fronds). 



