The multigroup transport equation is studied in plane geometry assuming that the transfer kernel is representable in a degenerate form. The eigenvalue spectrum is analyzed and the associated eigensolutions are obtained in terms of generalized functions. Full-range orthogonality relation is demonstrated. The full-range completeness of the eigensolutions is established under rather general conditions. For the half-range completeness to hold, it is additionally required that the scattering kernel be self-adjoint and possesses reflection symmetry.