CHARACTERISTIC DEEP-SEA TYPES. - - SPONGES. 179 



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

 round or angular. 



One of the most abundant sponges 

 is the small Radlella 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 



O L / .--.' 



a fringe of needles, with a layer of larger 

 needles radiating from the centre of 

 the disk and forming the base. Fig-. 545. R^dieiia sol. f. 



. 





