ILLUSTRATIONS. 



Plate I. 



Shore of an estuary showing a mud tower raised by a Thalassina over the mouth 

 of its burrow. 



TEXT FIGURES. 



Fig. 1. Section to show the plan of a Thalassina burrow excavated July 4. 

 Distance from surface of ground to bottom of burrow about 1.2 meters. 

 2. Diagram showing a plan of the mouth of a Thalassina burrow excavated 

 July 2; the distance from a to a; was about 0.73 meter, the depth at 

 the water level, 0..30 meter below the surface of the ground, a, open 

 entrance ; 6, closed enti'anee. 



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