Binary combinations of the fullerenes C-60 and C-70, in molar ratios spanning the concentration interval between the two pure components, were crystallized from dilute benzene solution to study their copacking in the solid state. From electron diffraction patterns, the hexagonal close packed structure was found to persist across the entire concentration interval, becoming more and more disordered when higher concentrations of C-70 were present. The ordered face-centered cubic structure of C-60, with crystals oriented along [111], disappeared when C-70 was present at a molar concentration somewhat above 0.40. At high C-70 concentrations (including the pure material), electron diffraction patterns indicated that a new primitive cubic structure, with a unit cell spacing a = 10.63 Angstrom, might be present, even though such a molecular packing should not be energetically favored. It is shown, however, that such patterns can be produced when initially solvated three-dimensional crystals collapse to form a randomly displaced packing (shear direction : [110]) of primitive square lattice layers as the solvent is rapidly evaporated. The disordered structure is, therefore, a distortion of the C-70 fcc crystal structure oriented along [001].