[Haskell-cafe] difference between type and newtype

Hello! I cannot understand this piece of code: type Z = Int type T a = Z -> (a, Z) newtype T1 a = T1 (Z -> (a,Z)) mkT :: a -> T a mkT a = \x -> (a, x) mkT1 :: a -> b -> (a,b) mkT1 a = \x -> (a, x) why mkT is a type constructor and mkT1 seems not to be? thanks for your kind attention. Andrea