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THE AMERICAN NATURALIST [Vol. LII 



The Alcyonacea, organ-pipe and blue corals, are repre- 

 sented in Hawaii by only five species ; the Gorgonacea, 

 sea-fans, by 16 species; and the Pennatulacea, sea-pens, 

 by 48 species. Many of the Hawaiian members of these 

 groups are of great beauty, but are never found in situ 

 on the reefs, and when rarely washed ashore are badly 

 mutilated by the waves. Some of the species are phos- 

 phorescent. 



The typical Hawaiian fringing reef exhibits five dis- 

 tinctive biological zones. This zonation parallels the 

 shore-line, and is best developed on those reefs which 

 possess wide lagoons and a well-defined outer margin or 

 rim. 



1. Beach or Inshore Waters.-The shallow inshore 

 waters, varying in depth from 6 to 36 inches, sustain a 

 number of the quiet-water alga?, such as Euteromorpha 

 spp., Hypnea nidifica, Gracilaria, Chcetomorpha, Viva, 

 Chondria, Lmgora, etc. The bottom is of coral sand or 

 mud, more or less contaminated by volcanic soil washed 

 from the lowlands. The water is often mingled with rela- 

 tively high percentages of fresh water. The nature of the 

 bottom depends largely upon the proximity of fresh- 

 water streams and of the reef-rim. In manv places 

 where the surf is heavy and reef material abundant, the 

 bottom is pure white coral sand, with practically no rock 

 or mud. In other districts there are large mud-flats ex- 

 posed at low tide; the limestone pavement is covered with 

 a thin sheet of mud, with little sand. Every gradation 

 may be found between these two extremes. At the mouths 

 of streams and at numerous other places along the coasts 

 where fresh-water springs exist below tide-level, the in- 

 shore water is so fresh as to prohibit the development of 

 the strictly marine species. 



2. Partially Submerged Rocks.~In some places the 

 beach and shallow waters are devoid of rock masses, but 

 in general one finds partially submerged rocks scattered 

 all along the coasts. These may be either close inshore, 

 in the form of ledges or detached fragments, or may lie 



