Read geometry from JSON object

In Flex 3, I convert a featureset (including several simple polygons) to JSON object: var geomJSON:Object = myFeatureSet.toJSON();

Then I pass the geomJSON as a parameter to a web service (developed using VS2010 C# language). Now the problem is: how to read the polygons inside the C# web service? What kinds of ESRI classes should I use?

Many thanks in advance!