FERMILAB-COLLIDER. Search for pair production of a fourth generation charge -1/3 quark (BQPRIME) in pbar-p collisions at a centre-of-mass energy of 1.8 TeV. BQPRIME quarks are assumed to decay via flavour changing neutral currents. The search uses the signatures (gamma+3jets+mutag) and (2gamma+2jet). No significant excesses above background are seen. Upper limits to the production cross sections are given. DE = D0.