FLC OF A B737-200 FAILED TO MAKE A XING RESTR DUE TO A MISUNDERSTANDING AND COORD BTWN THE FLC AND THE ACTUAL FIX GIVEN BY ATC. THE ROUTING TO WHICH THE FLC WERE CLRED WOULD NOT HAVE TAKEN THEM OVER THE XING FIX IN THE FIRST PLACE. THEREFORE; EVEN THOUGH THE FO READ BACK THE CLRNC; AND THE CAPT SEEMINGLY RESPONDED TO IT; THE CAPT BELIEVED THE FIX TO BE THE VOR TO WHICH THEY WERE HEADED.

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ENRTE TO STL FROM MCI; ZKC CLRED US DIRECT TO FTZ VOR. NORMALLY WE GO OVER KAYLA INTXN (FTZ 275 DEG RADIAL; 11 MI) THEN FTZ ON THE TRAKE ARR INTO STL. ZKC THEN CLRED US TO CROSS KAYLA INTXN AT 11000 FT AND 250 KTS. WE WERE ALREADY DIRECT TO FTZ VOR ON THE 275 DEG RADIAL WHICH DOES NOT TAKE US OVER KAYLA INTXN. SINCE WE WERE NOT GOING OVER KAYLA; I HAD MY MIND TUNED IN TO THINK THEY WANTED US TO CROSS FTZ VOR AT 11000 FT AND 250 KTS. WE DID NOT CATCH THIS MISTAKE OR ASK ATC FOR A DIFFERENT XING RESTR SINCE WE WERE NOT GOING OVER KAYLA INTXN. APPROX 4 MI FROM FTZ VOR ON STL APCH; APCH ASKED IF WE HAD BEEN GIVEN A XING RESTR AT KAYLA. AT THIS POINT WE WERE LEVEL AT 11000 FT; 250 KTS. WE RESPONDED 'YES' REALIZING OUR MISTAKE. WE TOLD ATC THAT WE WERE NEVER OVER KAYLA INTXN AS WE HAD BEEN CLRED DIRECT TO FTZ VOR. ATC RESPONDED 'NO PROB.' WE SHOULD HAVE CAUGHT THE MISTAKE INITIALLY WHEN ATC CLRED US TO CROSS KAYLA INTXN AT 11000 FT; 250 KTS; SINCE WE WERE NOT GOING OVER KAYLA. ATC SHOULD NOT HAVE GIVEN US THE XING RESTR AT KAYLA SINCE THEY HAD CLRED US PREVIOUSLY TO FTZ VOR WHICH WOULD NOT TAKE US OVER KAYLA INTXN.