KEY TO THE GENERA. 131 



S- Fronds regularly forking, thin, narrow ; sides of 

 lobes parallel, ends rounded. 

 (o.) Dull red, not adhering. Rhodymenia. 

 (^.) Brilliant red; interrupted midrib of darker 

 color, or fruit dots scattered over the 

 surface ; adheres. Stenogramma. 



II. Frond flattened or compressed. 

 I. Frond pinnately branched. 



(a.) Frond narrow, dense, hard, dark red. 

 Primary branches, alternate or forking; 

 secondary, short, tapering to both ends, 

 pinnate. Prionitis lanceolata. 



(b.) Frond narrow, cartilaginous, divided into 

 several branches; pinnae and pinnulae, 

 alternate, blunt at apex; duU purple. 



JLaurencia. 



(c.) Pinnse, arranged on the edges of the 

 main stem and long branches, short, the 

 opposite ones unlike. Ptilota. 



(d.) Frond very narrow, homy when dry ; main 

 branches irregular; pinnae and pinnulse 

 exactly opposite, with wide rounded 

 axils, ultimate pinnae tapering to both 

 ends; purple, often faded. Gelidium. 



