branches, in the space between the pinnae or from the edges of the pinnae 

 themselves ; they vary much in shape, even on the same specimen, ovate, 

 ovate-acuminate, or cuspidate, and linear-lanceolate, occurring frequently to- 

 gether. Their substance is densely cellular, and they are closely covered, 

 on both surfaces, with tubercles, pierced with a pore, beneath each of which 

 is an ovoid spore-cavity, bearing both spores and antheridia ; the former 

 attached to the walls, the latter to branching filaments, and both are sur- 

 rounded by simple paranemata. The spores are nearly egg-shaped, with a 

 wide perispore. The substance is coriaceous, becoming rather brittle when 

 dry ; when recent the frond contains a large quantity of mucus, which is 

 discharged in fresh-water. The colour is a greenish-olive, becoming rusty 

 in age, and reddish-brown when dried. 



Under Plate IV. we have already remarked the strong re- 

 semblance between the subject of that and of the present Plate ; 

 the chief difference (colour and substance excepted) being in the 

 form of the receptacles. 



Professor J. Agardh separates our S. dorycarpa into two spe- 

 cies, distinguished by the comparative length and form of the 

 receptacles ; but I find it impossible to hold up these forms, 

 even as varieties, and believe that the characters observed by 

 Agardh depend altogether on the depth of water at which the 

 plant vegetates. The form called S. sciphocarjpa, when truest to 

 its type, is cast up from deep water. The ordinary S. dorycarpa, 

 with ovate or ovate-lanceolate receptacles, occurs about low- 

 water mark, or in rock-pools, between tide-marks ; in the latter 

 case being much stunted in growth and very densely ramified. 

 Specimens connecting the two extreme states may easily be 

 found. 



Fig. 1. Scytothalia dorycarpa ; portion of a frond, — the natural size. 2. 

 Receptacles, of various forms. 3. Section through a spore-cavity. 4. A 

 spore : — the latter figures variously magnified. 



