134 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



This belt bordering the typical marine zones is charac- 

 terised by winding channels and innumerable " pans," whose 

 history is traced in the paper above-mentioned. These " pans " 

 contain a curious assemblage of insect larvae and marine 

 animals, among those noted being Sphaeroma, Garnmarus, 

 small Carcinus, larval fish, young eels, Paludestrina, etc. The 

 Salicornetum is an open association on bare silt and is 

 often absent, the whole or part being occupied by sand dune, 

 shingle, etc., with their respective faunas. 



The Salicornetum is always, in my experience, too firm 

 'for Cardium and Macoma, and the fauna includes great numbers 

 of the little Paludestrina stagnalis (Hydrobia ulvae), the 

 burrowing crustacean Corophium volutator (grossipes), a few 

 small Arenicola, Nereis diversicolor and a few Littorina littorea. 

 This association passes into the more marine conditions of the 

 cockle beds proper. 



Petersen* in discussing the animal communities of the 

 level bottom designates this zone the Macoma or Baltic Com- 

 munity, and states concerning it, " One community, the 

 Macoma, seems to be altogether independent of the composition 

 of the level bottom, living equally well on pure sand .... 

 and on pure mud .... temperature and salinity are likely 

 to be of importance." He ascribes the great abundance of 

 bivalves in this zone to the absence of Echinoderms. " In the 

 communities where Amphiura spread their arms abroad 

 forming a network on the bottom, extremely few bivalves are 

 found ; the young being devoured. In the shallow coastal 

 waters, etc., where Echinoderms are few or absent these young 

 can persist, though the great majority never attain full growth 

 and may be killed by wave action, etc. (probably the very 

 factors that eliminate the Echinoderms). It is in such places 

 that the Macoma communities can live and thrive continually, 



* Petersen, C. G. J., " The Sea Bottom and its production of Fish Food," 

 Report Dan. Biol. Station, 1918. 



