Corrected I‐band absolute magnitude vs. the logarithm of the maximum 21 cm rotation velocity. Squares indicate late spirals; triangles indicate early spirals. The solid line is the inverse unweighted fit to all the points (﹩n=128﹩), the dashed line is the fit to the late spirals only (﹩n=37﹩), and the dotted line is the fit to the early spirals (﹩n=91﹩).