60 MARINE ALGAi 
ramified. The frond consists of a prostrate stem, from the lower 
side of which root-like fibers or holdfasts descend into the hard 
sand or coral, and from the upper side leaf- and branch-like 
secondary fronds arise. These plants grow luxuriantly in tropi- 
cal waters, extending over large surfaces, and are the chief food 
of turtles. (Plate VIIL) 
C. prolifera. Frond or lamina flat and leaf-like, two to four inches 
long, one half to three quarters of an inch wide, either simple or once 
forked ; margin entire. Similar lamine spring from the surface or from 
the edge or base of the different leaf-like portions. Lamine rise from 
the upper side of the creeping, rooting stem. Its substance is somewhat 
horny and translucent. 
C. Mexicana. Prostrate, creeping stem, with rootlets or holdfasts 
below, and leaf-like fronds above; fronds simple or with one or two 
branches deeply cut in narrow lobes nearly to the center. The species 
abounds at Key West. (Plate VIII.) 
