480 



PllOCEEDINGS OF THE AMERICAN ACADEMY. 



frequently contain coral mud and diatoms. Doubtless it is protected 

 at low tide by its denseness, which mitigates desiccation. The name 

 refers to its humble appearance. 



Trophosome. Colonies are a deep horn color, pinnate, unfascicled, 

 thirty to forty millimeters long. The sometimes geniculate stem is 

 constricted below each of the ten or more alternate pinnae (Figure 32). 



Three sessile hydrothecae usually found on each joint of stem, most 

 frequently two on the same side as the pinna, the other sub-opposite 

 the more distal. Variations in arrangement are found, such as two pairs 



Figure 32. Sertularella humilis. Part of main stem and branch (X 25). 



of opposite hydrothecae on a joint. The flattened pinnae with two or 

 three pairs of opposite, or slightly sub-opposite, hydrothecae to a seg- 

 ment. Base of stem and pinnae devoid of hydrothecae. 



Hydrothecae of stem and pinnae tubular and two or three times as 

 long as wide for the lower two thirds of their length, and at the base 

 confluent with the stem. Above, bending outward at an angle of 

 thirty-five to forty-five degrees, and also slightly toward each other. 

 On this side the intervening space usually not so wide as a hydrotheca, 

 though width increases with age. Outer border of hydrotheca con- 

 tinuous with border of stem or pinna, which extends proxiraally for a 

 short distance to the next hydrotheca or constriction. The confluent 



