35 



Cymodocea. A pulpy stem, marked with rings in 

 the lower part, and smooth in the upper. Cells fili- 

 form, alternate or opposite. 



GENERA. 



BELONGING TO THE THIRD ORDER OF THE FIRST CLASS. 



Tibiana. Branches in zig-zags. Polypous openings, 

 placed alternate, and on the sides, at the summits^^of 

 the angles. 



Naisa. In fresh water. Polypi with each a single 

 row of tentacula, generally ciliated. 



Tubularia. Tubular, simple or branched. A soli- 

 tary polypus at the extremity of each branch. 



