Finding Chart. Left panel: the Perseus-Taurus region as seen with Planck E(B-V) dust (Abergel et al. 2014). The Taurus and Perseus molecular clouds are indicated (as defined in Zucker et al. 2021). Right panel: 2D projection of 3D density structures (densities n > 15 cm⁻³) based on L20's 3D dust map. While on the plane of the sky (as well as in velocity space; see Figure 4(a)), the Perseus and Taurus clouds seem to connect, in practice they are separated by ≈150 pc along the LOS. As we discuss in this Letter, the two clouds are still related, as they both lie on two opposing ends of a large 3D shell, the so-called “Per-Tau Shell.”