PLATE XVIII. 



Figs. 1,2 a. Mertensides hullatus, (Bunb. species). Pages 35 to 39. 



Fig. 1. Portion of the lower part of a compound fertile pinna, showing the pinnules with undu- 

 late margins, and the increase of sori towards the middle and summit portions of the 

 ultimate pinnse. 



Fig. 2. Portion of a compound fertile pinna with fully fructified pinnules. A common form. 



FlG. 2 a. Pinnules of Fig. 2, magnified to show the fructification. 



