OrnivER.— Marine Littoral Plant and Animal Communities. 517 
life are recognized—namely, the subsurface, or burrowing, organisms; the 
surface, or crawling, animals; and, when a plant is dominant, the supra- 
edaphic plant-form and its dependent life. On rocks in the shelled-animals 
according to the dominant growth-forms. Thus the shelled-animals forma- 
tion includes four subformations—pelecypod, sessile cirripede, tubicolous 
polychaet, and gasteropod. Each of t ese comprises one or more 
composition. Differences in the principal species might utilized to 
define subassociations, but I have not treated the subject in such detail 
in the present paper. 
CLASSIFICATION OF LITTORAL Brotic COMMUNITIES. 
Opposite change take place. Littoral formations, therefore, can be classed 
