IT is well known that the transformation theory of quantum mechanics corresponds to the property of the classical equations of motion of being invariant with respect to contact transformations. These are simultaneous transformations of co-ordinates xk (including time) and momenta pk (including energy), such that the difference of pkdxk in the old and in the new variables is a total differential. The point transformations in the x-space are only a special case ; but there exists another case of the same simplicity which can be described as a point transformation in the p-space.