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THECATA. 
I. Sheath slightly calcareous ; cells single, or in rows. 
1. Sheath slightly calcareous, cells enlarged, in rows, united or single. 
— Gel LARI AD^. 
a. Cells united. 
h. Cells with the orifices opening on the upper surface. 
Cellularia. 
Tricellaria. 
Crisia. 
hh. Cells in pairs, attached by the back, the orifices with 
opposite aspects. 
Notamia. 
aa. Cells single. 
Eucratia. 
Anguinaria. 
II. Sheath membranaceous, cells enlarged externally and lateral . — ■ 
Sertulariad^. 
I. Base of the cells broad, coalescing with the stem. 
a. Cells on opposite sides of the stem. 
Sertularia. 
Dynamena. 
Thuiaria. 
aa./ Cells unilateral. 
Antennularia. 
Plumularia. 
Serialaria. 
II. Base of the cells narrow, or pedunculated. 
Campanularia. , 
Valkeria. 
Cymodocia. 
III. Sheath membranaceous, the cells are the simple extremities 
of the branches.««TuBULARiADA:. 
Tubularia. 
Plumatella. 
