CETERACn. 151 



Genus VIII. CETERACH, or SCALE FERN. 



Of the genus Ceterach there is only one British species, 

 and this is so different from all others as to be distinctly 

 recognized at a glance. The mark by which it is known 

 is this : — the back of every frond is covered by densely- 

 packed, brown, pointed, chaffy scales. Among these 

 scales, and concealed by them, lie the elongate sori, which 

 are anomalous, in regard to their relationship, in having 

 no indusium. The affinity of Ceterach is without doubt 

 with i\iQ Asplenium-\\ke Ferns ; and this being the case, 

 they ought to have an indusium ; the Polypodium-\\VQ and 

 Acrostichum-Y\\iQ Ferns chiefly, among the dorsal groups, 

 wanting this cover to the sori. No indusium, however, 

 exists here, unless it be represented by a kind of mem- 

 branous ridge, which is to be found on the receptacles just 

 behind the sori, and is the part which has been sometimes 

 called an indusium. The probability is, that it does 

 represent that organ, which is not largely developed in 

 consequence of the presence of so dense a covering of scales, 

 these not only serving the purpose of a cover to the sori. 



