  We classify line nodes in superconductors with strong spin-orbit interactions
and time-reversal symmetry, where the latter may include non-primitive
translations in the magnetic Brillouin zone to account for coexistence with
antiferromagnetic order. We find four possible combinations of irreducible
representations of the order parameter on high symmetry planes, two of which
allow for line nodes in pseudo-spin triplet pairs and two that exclude
conventional fully gapped pseudo-spin singlet pairs. We show that the former
can only be realized in the presence of band-sticking degeneracies, and verify
their topological stability using arguments based on Clifford algebra
extensions. Our classification exhausts all possible symmetry protected line
nodes in the presence of spin-orbit coupling and a (generalized) time-reversal
symmetry. Implications for existing non-symmorphic and antiferromagnetic
superconductors are discussed.
