There's a bit of a misunderstanding here. The lithosphere actually includes the uppermost part of the mantle.

Here's a breakdown:

* Lithosphere: This is the rigid, outermost layer of the Earth. It includes the crust (both oceanic and continental) and the uppermost, rigid part of the mantle. It's broken up into tectonic plates that move and interact with each other.

* Mantle: This is the layer beneath the lithosphere. It's mostly solid rock, but it behaves like a very viscous fluid over long periods. The mantle is divided into the upper mantle (which includes the lithosphere) and the lower mantle.

So, there's no distinct layer between the mantle and the lithosphere. The lithosphere is simply the rigid, uppermost part of the mantle.