posure through pink to a dirty white. Substance soft, spongy ; when young, 

 rather gelatinous and adhering to paper; when old, dry and rigid. 



Notwithstanding the robust and sponge-like frond, the plant 

 here figured is so closely related in many respects to Crouania, 

 that it may be questioned whether it ought to be kept generically 

 distinct. Compared with C. attennata, indeed, the resemblance 

 is not very striking, but large specimens of C. vcstita very much 

 resemble the narrower and more branching fronds of Ptilodadia ; 

 nor is there any very essential character between the two genera. 

 There is no diflFerence in fructification; and the more or less 

 compressed branches, and firmer, less gelatinous substance, are 

 purely specific characters. I have not been able clearly to make 

 out the anastomosis of the ramelli described by Sender and J. 

 Agardh ; this character, if really present, must be held to be the 

 most absolute, as distinguishing Ptilodadia from Crotiania. 



Fig. 1. Ptilocladia pulchka, — the natural size. 2. Cross section through 

 a branch, showing a section of the central axile filament, the peripheric ra- 

 melli and some tetraspores in situ. 3. Apices of a raraellus, with an attached 

 tetraspore. 4. External view of one of the ultimate divisions of the frond, 

 containing a pair of favellce : — magnijied. 



