PLATE XIII. 

 [Proc. Wash. Acad. Sci., Vol. Ill, PI. XXIV.] 



FIG. I. Sertularella saccata Nutting. Part of colony, showing hydrothecae and 

 gonangia with acrocysts (enlarged). 



2. Three hydrothecae (still more enlarged). 



3. Single hydrotheca, showing operculum (drawn to same scale as fig. 2). 



4. Thuiaria fabricii (Levinsen). Part of branch showing hydrothecae and 

 gonangia (enlarged). 



5. Front view of part of branch (enlarged). 



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