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UNITED STATES NATIONAL MUSEUM BULLETIN 251 



in thickness and the coloration of colonies varies considerably accord- 

 ing to the amount and the physiological condition of zoochlorellae and 

 Cyanophyceae embedded in the test. They are light grayish white, 

 faintly greenish, or light brownish. Some colonies show brownish, 

 yellowish brown, pinkish, or bright greenish tint. Colonies are usually 

 encrusting the surface of some algae and thus their shape is quite irreg- 

 ular. No system is found in the arrangement of zooids. 



Various amounts of zoochlorellae and a few Cyanophyceae are 

 embedded in the test itself, not in the lacunae system. The former are 

 rather small, 7.5-10/* in diameter; while the largest filament of the lat- 

 ter found in examined colonies is 68/x in length. In addition, a large 

 amount of stellate calcareous spicules are distributed evenly and 

 densely throughout the test from surface to bottom. The surface of 



Figure 29. — Trididemnum viride (Herdman): a, spicules, consisting of many rays, X 940; 

 b, spicules, consisting of fewer rays, X 940; c, cyanophyceae contained in the test, 

 highly magnified; d, right side of a zooid; e, right side of a larva. 



