A B737-300 CAPT; PNF; ON APCH TO SMF; DID NOT PROMPT HIS FO TO CONTINUE THE DSCNT AS ADVISED BY ATC.

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WE'RE ESTABLISHED ON THE WRAPS FIVE ARR TO SMF AND ZOA TELLS US TO 'CROSS TURLO AT OR BELOW FL280; THEN PLT'S DISCRETION TO FL240.' AFTER STARTING OUR DSCNT; WE ARE SWITCHED TO A NEW ZOA CTLR. AS WE CROSS TURLO AT FL280; THE NEW CTLR TELLS US TO 'CONTINUE OUR DSCNT TO CROSS TWANE AT 11000 FT.' THE FO; NOT FULLY UNDERSTANDING THE NEED TO KEEP THE DSCNT GOING; LETS THE PLANE LEVELOFF AT FL280 AND WAITS FOR THE VNAV PATH TO START THE DSCNT. AFTER ABOUT 30 SECONDS; I NOTICED THAT VNAV PATH WAS NOT GOING TO INITIATE THE DSCNT ANYTIME SOON AND TOLD HIM SO. ABOUT THE SAME TIME; THE CTLR RESTATED THE NEED TO START THE DSCNT TO STAY CLR OF XING TFC. THE FO STARTS HIS DSCNT AND STAYS CLR OF THE XING TFC AND CROSSES TWANE AT 11000 FT. THE FO DIDN'T FULLY UNDERSTAND THE CTLR'S CLRNC TO 'KEEP THE DSCNT GOING.' I DIDN'T INTERVENE IN A MORE TIMELY FASHION WHEN IT WAS CLR TO ME THE FO WAS GOING TO WAIT FOR THE VNAV PATH TO START THE DSCNT. WE SHOULD HAVE BOTH VERBALLY CONFIRMED WHAT THE CLRNC WAS. THE PF SHOULD CONFIRM AND TELL THE OTHER CREW MEMBER WHAT MODE OF DSCNT HE WILL USE TO SATISFY THE CLRNC. BETTER TERMINOLOGY FROM THE CTLR; SUCH AS; 'I NEED YOU TO START YOUR DSCNT NOW FOR XING TFC; WOULD HAVE BEEN HELPFUL.