CETERACII. 153 



developed fronds, prettily contrast with the deep green of 

 the upper surface. The pinnsB or lobes are of an ovate 

 form, and either entire or lobed on the margin. 



The opacity of the fronds renders the venation indis- 

 tinct, and indeed it is only to be made out by examining 

 young fronds, removing the covering of scales, and the 

 outer skin of the frond itself. It is then seen, that from 

 the lower corner the principal vein enters, taking a sinuous 

 course towards the upper side of the apex ; it branches 

 alternately, the veins being again branched, and the 

 venules becoming joined more or less near the margin. 

 The sori are borne along the sides of the venules in a very 

 irregular manner, the majority of them being directed 

 towards the apex of the pinna. At first, the sori are 

 quite concealed by the scales, but the spore-cases ulti- 

 mately protrude between them, although, being very similar 

 in colour, the latter are never very obvious. 



The Ceterach is a mural species, occurring on the walls 

 of old buildings and ruins, and in rocky places. It is 

 pretty generally distributed in the United Kingdom, but 

 is considered somewhat rare in Scotland. It occurs also 

 throughout central and southern Europe, and in the north 

 of Africa. In the Canaries, a closely-allied but much 



