记数列\(\{a _{n} \}\)前\(n\)项和为\(S _{n}\),若\(1\),\(a _{n}\),\(S _{n}\)成等差数列,且数列\(\{ \dfrac {a_{n+1}}{(a_{n+1}-1)(a_{n+2}-1)} \}\)的前\(n\)项和\(T _{n}\)对任意的\(n∈N*\)都有\(T _{n} -2λ+1\geqslant 0\)恒成立,则\(λ\)的取值范围为\((\:\:\:\:)\)
A.\((-∞ , \dfrac {1}{6} ]\)
B.\((-∞ , \dfrac {1}{2} ]\) C.\((-∞ , \dfrac {5}{6} ]\) D.\((-∞ , 1]\)