This essay highlights 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 especially seeks to bring out how aquatic figures of dissociation and dissolution that surface in these authors’ virtualized marine environments structure important ways in which culture has been thought, felt, imagined, and otherwise experienced. It attends especially to the amphibious life of mermaids and mermen, which emblematizes, it argues, the idea of culture when it allegorizes the movement of thought across boundaries between the human and the inhuman, the social and the natural.