The tortoise shell occupies a remarkably diverse symbolic register across the depth-psychology corpus, appearing as cosmological support, divinatory instrument, musical origin, and lunar emblem. In the Hermetic literature—Kerényi, López-Pedraza, and the Homeric Hymn to Hermes—the shell is the raw material from which Hermes fashions the first lyre, making it the primordial site where instinct is transmuted into culture and chaos into resonance. Kerényi reads the tortoise as ‘the most ancient creature in the world,’ borne by cosmologies from China to India to Mesoamerica as the subterranean support of the entire cosmos, a manifestation of Vishnu, the floor of Tartarus. In the I Ching commentaries, tortoise shell functions as an instrument of infallible divination whose authority can paradoxically be superseded by ‘right principles’—a tension Wang Bi’s tradition exploits extensively. Neumann situates the tortoise among the lunar, backward-moving creatures of the Great Mother’s negative aspect—alongside crab and snail—symbols of concealment and cyclical withdrawal. Easwaran’s Bhagavad Gita commentary deploys the shell as a figure for pratyahara, the yogic withdrawal of the senses, linking containment with freedom. These strands—musical origin, cosmic support, oracular instrument, and protective enclosure—collectively make the tortoise shell one of the corpus’s richest images of the boundary between inner and outer worlds.