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 hydrothecse (still more enlarged). 



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



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

 gonangia (enlarged). 



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



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