422 



THE AMERICAN NATURALIST 



[Vol.LII 



dria, Laurencia, Martensia, Champia, Wrangelia, Galax- 

 «ura, Padina, Sphacelaria, ILidrodotlmis, etc. 



4. The Lagoon.— The entire region between the beach 

 line or strand and the seaward rim of the reef is properly 

 designated as the lagoon, but for the purposes of this de- 

 scription the term will be restricted to the deeper waters, 

 which are usually located about midway between the beach 

 and the reef-rim. As one approaches the lagoon wading 

 becomes impossible, the water deepens to eight, twelve or . 

 twenty feet, but again becomes shallow as the outer edge 



of the reef is reached. The water of the lagoon is placid, 

 clear, and in normal weather very translucent, so that the 

 bottom receives good illumination. Although a number 

 of the smaller algae grow upon the floor of the lagoon, the 

 region is comparatively barren as compared with the shal- 

 lower waters on either side. The lagoon floor is a region 

 of coralline and animal life, rather than of plant life. 

 The quantities of sand and silt that are constant! v washed 

 over the floor from the disintegrating reef-rim render it 

 difficult for plants to maintain themselves. The floor is 

 so irregular in topography that collecting is very difficult; 



