Abstract
Boulders of fossil corals and rocks near the Panamá Canal were investigated. Lowest down the boulders were smooth and yellow-green from microscopic algae, upmost smooth and dark-coloured, and in between pitted and light-grey. There is probably no causal relationship between structure and colour; both might be the result of the same agents. The species found, enumerated in an Appendix, were mostly the same as at similar localities in Columbia. There was good agreement in vertical distribution in the two areas, though the relative height could be different due to differences in exposure. The zonation was less distinct in Panama because some stations were so small that the specimens found there were too few to give impression of zones. Lowest down was a lithothamnia zone followed by a poorly developed zone of mixed algae, on the boulders in the yellow-green area. Contrary to Colombia there was no zone of algal mat and no Palythoa zone. A barnacle-vermetid zone occurred at some stations but within the zone of mixed algae, where other species, too, formed more or less distinct belts. No distinct zonation was observed higher up. The transition beween what corresponds to the spray and maritime zones in Columbia was gradual.