1918] MACCAUGHEY—HAWAIIAN ALGAE 47 
are either of consolidated reef coral or of black basaltic lava. Some 
algal species show a preference for the coral (Sargassum, Gracilaria, 
Laurencia), others for the lava blocks (Gelidium, Alnfeldtia, etc.). 
The rocks may be in somewhat protected situations, or may be 
exposed to the full force of the surf. The alga flora will depend 
largely upon the situation of the rocks with reference to the surf. 
The following kinds occur on rocks which are exposed to the con- 
tinual battering of the surf: Gymmnogrongus spp., Asparagopsis 
Sanfordiana, Codium spp., Sargassum spp., Dictyota acutiloba, 
Haliseris plagiogramma, Gelidium spp., Alhnfeldtia concinna, 
Porphyra leucosticta. The controlling factor in the alga flora of 
the partially submerged rocks seems to be the circulation of pure, 
well oxygenated sea water. Rocks in stagnant or impure water sup- 
port a scanty flora as compared with those in surf-swept localities. 
3- Pools.—Passing out beyond the rock litter we come to a zone 
characterized by numerous pools or pockets. These cuplike 
depressions in the lagoon floor vary in size from little pockets a 
meter in depth and diameter to large pools 5-10 m. in depth and 
diameter. The pools are easily distinguished by the darker tint 
of their waters as contrasted with that of the shallow lagoon. 
These pools in the floor of the lagoon are not to be confused with 
the “tidal pools” along the beaches. The lagoon pools are in- 
habited by a variety of algae and animals that prefer these shadowy 
havens to the exposure of the shallows or the outer reef. The 
bottom of the pool may be covered with clear coral sand, or coral 
débris, or masses of growing coral; its alga flora will depend upon 
its depth and the resultant intensity of illumination. 
The following are typical forms that inhabit the lagoon pools: 
Lithothamnion spp., Corallina spp., Peyssonnelia rubra, Grateloupia 
Jilicina, Ceramium clavulatum, Amansia glomerata, Polysiphonia 
SPP., Chondria tenuissima, Laurencia spp., Martensia flabelliformis, 
Champia compressa, Wrangelia penicillata, Galaxaura lapidescens, 
Padina pavonia, Sphacelaria furcigera, Hydroclathrus cancellatus. 
4. Lagoon.—The entire region between the beach line or strand 
and the seaward rim of the reef is properly the lagoon, but for the 
Purposes of this paper the term will be restricted to the deeper 
waters, which usually lie about midway between the beach and the 
