The detection of granular superconductivity in Pr222Nb-10 leads to the conclusion thatR2−zCezCuO4(R21-4) compounds andR2−zCezSr2Cu2NbO10(R222Nb-10) compounds both superconduct forR=Pr.The fact that Gd21-4 does not superconduct, but Gd222Nb-10 does, indicates that the superconducting layers are different in the two classes of compounds. Magnetic resonance studies of Gd222Ru-10 and Gd21-4 indicate either that ordered magnetism and superconductivity co-exist in the cuprate-planes or else that the cuprate-planes are not the primary superconducting layers in Gd222Ru-10. ©1999 American Institute of Physics.