This essay shows how marine imagery mediates thought about culture, by exploring a series of imagined submarine visions across an intertextual network that extends from Matthew Arnold’s poem “The Forsaken Merman” back to Hans Christian Andersen’s fairy tale “The Little Mermaid,” across the Atlantic to William James’s writings, and thence to essays and poetry by Arnold’s successor as a water-obsessed, culture commanding poet-critic, T. S. Eliot. The essay seeks to bring out how aquatic figures of dissociation and dissolution surface in these authors’ virtualized marine environments, and there structure ways culture has been thought, felt, imagined, and otherwise experienced. It attends especially to the amphibious life of mermaids and mermen. These figures emblematize the idea of culture when they allegorize the movement of thought across boundaries between the human and the inhuman, the social and the natural.