In myth, Echo lives in hollow places. Gaston Bachelard advances the shell as one of those locations. W.B. Yeats and Paul Valéry, however, deploy it as a physical object and a poetic trope. For them, the shell is a figure of echo of both poetry and subjectivity. Yet where Yeats uses the figure in his poetry, namely his juvenilia, Valéry devotes a philosophical treatise to the mollusk. Both collude and collide in their examination and figuration of the shell. If Yeats associates it with his own poetic growth, that is, as a figure of self-appraisal through self-echoing, Valéry considers this "marvelous thing" a perfect occasion for the mind to engage in a philosophical inquiry into the origins of poetic and metaphysical genesis and destination. Here conchology rhymes with phenomenology. The shell, as an echoic trope, rectifies Yeats's aesthetic and even political trajectory. In Valéry, however, the observer's inquiry is left unresolved. Poetic genesis remains as enigmatic as the shell's and self 's inner formation.