The translational diffusion coefficient D was determined from dynamic light scattering measurements for atactic polystyrene (a-PS) in cyclohexane at various temperatures ranging from 30.0 to 45.0 degrees C, above and below -, in the range of weight-average molecular weight M(w) from 1.27 x 10(6) to 6.40 x 10(6). The hydrodynamic-radius expansion factor alpha(H) determined from D is found to deviate from the first-order perturbation theory values even for small ($) over tilde z, indicating that its (first) coefficient of <($) over tilde z may be too large, where and is the scaled excluded-volume parameter defined in the Yamakawa-Stockmayer-Shimada theory for the perturbed helical wormlike chain. The present data for alpha(H) plotted against ($) over tilde z give a single-composite curve together with the previous ones for a-PS in toluene and in 4-tert-butyltoluene, confirming that the quasi-two-parameter scheme may be valid for alpha(H) as well as for the gyration- and viscosity-radius expansion factors alpha(S) and alpha(eta) irrespective of the solvent condition. It is also found that alpha(H) coincides with alpha(eta) within experimental error over the whole range of ($) over bar z studied.