EXPLANATION OF PLATES. 187 



PLATE II. 



Spirophyton typum. 



Fig. 1. Upper side of the frond, at about the sixth or seventh volution from the base. 



«« 2. A transverse section of the same individual, about two volutions lower than 

 fig. 1 ; looking upon the lower side. 



<« 3. A restored figure, showing the mode of growth. 



Spirophyton crassum. 

 Fio. 4. A view of the upper side of a volution of this species. 



