the node 'type' for SSS is inconsistant with the rest of the cycles api... Diffuse node is 'BSDF_DIFFUSE', Glossy node is 'BSDF_GLOSSY', SSS is 'SUBSURFACE_SCATTERING', however i would expect it to be BSSRDF_SUBSURFACE_SCATTERING or BSSRDF_SSS or something along those lines.
I have uploaded a blend file with a small python script to explain, hit run and look at the console.
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These just match the names of the nodes in the UI, if we add more SSS nodes they might be called things like 'SUBSURFACE_SCATTERING_SOMETHING'. The BSDF ones just happen to use a technical name because there isn't really any good name to describe them. We also don't call emission nodes EDF_ or so.