Roof Bars Question - Synergie / Evasion

I want to buy roof bars for my year-2000 Synergie / Evasion HDi SX.
My Citroen dealer says that two parts are needed. One is described in the accessories brochure as 'roof rails' (cost approx. ?90) the other is 'roof
bars' (cost approx. ?140)
The dealer knows nothing more about these parts, and I am having a problem imagining how the two parts will work. I presume that the item described as 'roof rails' is just an adaptor to fit into the roof gutter, rather than actual roof rails as fitted permanently to some other cars.
Can anyone advise?
I fitted Thule roof bars to my previous Xantia. These were not perfect because the bars were too long for the roof. This time I would prefer properly-fitting bars, which I imagine are available only from Citroen.

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