CHARACTERISTIC DEEP-SEA TYPES. SPONGES. 



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form : a thick, coarse, smooth sheet, with stout branches, either 

 round or angular. 



One of the most abundant sponges 

 is the small Radidla sol (Fig. 545), 

 which extends to over 1,000 fathoms 

 in depth. Its general appearance is that 

 of a segment of a sphere surrounded by 

 a fringe of needles, with a layer of larger 

 needles radiating from the centre of 

 the disk and forming the base. FiR . ^ 5 . - Radidia sol. f 



