specially designed latching apparatus 10 see fig1 e and 2 useable to releasably latch a firing head 12 see fig1 c 1e to a perforating gun 14 see fig1 f downhole within a subterranean wellbore 16 portions of which are illustrated in fig1 a and 1f representatively the wellbore 16 is lined in a conventional manner with a cemented in tubular casing structure 18 but the principles of the present invention are also applicable to uncased wellbores as subsequently described herein the latching apparatus 10 includes a tubular latching collar structure 20 see fig1 e and 2 that defines a lower end portion of the firing head 12 and a tubular stinger structure 22 see fig1 e and 2 having a pair of external j slots 24 formed on opposite external side portions thereof the stinger structure 22 defines an upper end portion of the overall perforating gun assembly the schematically depicted perforating gun 14 fig1 f is of a conventional construction and has a reduced diameter threaded upper end portion 26 which is connected to a threaded tubular crossover member 28 which in turn is threadingly coupled to the lower end of an outer tubular structure 30 used to lower the perforating gun 14 through the casing 18 to a predetermined depth therein adjacent a subterranean formation not shown to be penetrated as a result of firing the perforating gun 14 the upper end of the tubular structure 30 see fig1 a is threadingly coupled to the lower end of a tubing structure 32 extending to the surface extending upwardly from the perforating gun 14 is an extension tube 34 see fig1 e and 1f which is.