RIVULARIA. 265 



the filament. Colour pale chestnut, inclining to olive." 

 Carm. 



2. RAPHIDIA VIRIDIS Hass. 

 Plate LXIV. Figs. 3. 2. 



Char. Frond very mucous, soft. Filaments small, elongated. 

 Sheath not evident. 



/3 marginata. Filaments rather smaller. Sheath evident. 



Hob. Near Manchester : Mr. Sidebotham. Aberdeen : 

 Dr. Dickie. 



This Raphidia is very distinct. It was sent me by Mr. 

 Sidebotham of Manchester put up in fluid. The filaments 

 are not one half so large as those of R. angulosa, but much 

 longer ; the sheath in it could not be detected. In the variety 

 /3 the sheath was quite apparent, and I at first was induced to 

 regard it as altogether different : it is safer however to consider 

 it merely as a variety of R. viridis, or as that species in its 

 perfect condition, the sheath in the specimen sent by Mr. 

 Sidebotham, and which had been put up some time in fluid, 

 having probably become decomposed. 



Section iii. LITHONEMA Hass. 



Char. Fronds indefinite, truly ramose. Bases of the fila- 

 ments not manubriated. Filaments petrified. 



Derivation. From \i0os, a stone, and vrjfMi, a thread. 



1. LITHONEMA CALCAREUM Hass. 

 Plate LXV. Fig. 2. 



Char. Fronds large, orbicular, convex, afterwards aggregated 

 into a broad spongy crust zoned within, at length petrified. 

 Filaments slender, adherent, and dichotomously branched. 



R. calcarea Sm., E. B. t. 1799. ; Harv. in Hook. Br. Fl. 



p. 392. ; also in Manual, p. 150. 

 Hab. On rocks and stones in streamlets and the borders of 



subalpine lakes. 



