92 ON THE CLASSIFICATIOX OF FERX3. 



L POLYPODIACE^E. 



Sori round, without an indusium. 



1. POLYPODIUM. The sori dorsal, circular, and ex- 

 posed. 



2. ALLOSOEUS. Sori dorsal, roundish, and becoming 

 confluent beneath the margins of the frond. 



II. GYMNOGRAMME^E. 



Sori linear, without an indusium. 



3. GYMNOGRAMMA. Sori dorsal, linear, forked, 

 naked. 



III. ASPIDIE^E. 



Sori covered with a circular or roundish indusium, 

 springing from the back of the veins. 



4. ASPIDIUM. Sori dorsal, with circular, peltate, 

 or reniform indusia. 



IV. ASPLENIE^E. 



Sori covered with an oblong or elongated indusium, 

 which springs from the sides of the veins. 



5. ASPLENIUM. Sori dorsal, with a straight and 

 elongated indusium. 



6. SCOLOPENDRIUM. Sori dorsal, elongate, and placed 

 together in parallel pairs, the indusium opening along 

 the centre. 



7. CETERACH. Sori dorsal, hidden amongst rust- 

 coloured chaffy scales ; the indusium invisible. 



V. BLECHNE^E. 



The sori with an indusium forming longitudinal 

 lines between the midrib and margins of the pinnae. 



8. BLECHNUM. Sori dorsal, covered by a linear 

 indusium. 



