72 SQUIRTS, POLYPS, AND JELLY-FISHES. 



size to the dimensions of small polyps, and each 

 individual polyp secreting for itself an outer cover- 

 ing of lime and an inner series of lime partitions 

 (septa) corresponding to the fleshy ones that have 

 been described, you have before you the struc- 

 ture of a true coral, such as we find among the 

 great reefs of tropical waters. A single species 

 {Astrangia astrcefarmis), which forms encrusting 

 colonies on stone or shell from one to three inches 

 across, is found on our northern coast, and has been 

 occasionally picked yp on the l^ew Jersey shores. 



