The shear-induced concentration fluctuations in semidilute solutions comprised of ultrahigh molecular weight polyethylene (UHMWPE) as a solute and paraffin as a solvent were studied by shear-small-angle light scattering and shear-microscopy. In steady-state shear flow, a unique anisotropic scattering pattern was found to appear when the shear rate gamma is increased above a critical shear rate gamma(c). This anisotropic scattering pattern was found to be essentially identical to the "butterfly pattern" observed in high molecular weight polystyrene solutions in dioctyl phthalate. This butterfly pattern, found at temperatures higher than the equilibrium melting temperature of UHMWPE, suggests that the shear-induced concentration fluctuations or phase separation occurs in the homologous mixtures of UHMWPE and paraffin having characteristics of athermal solutions.