  We describe an extension of special relativity characterized by {\it three}
invariant scales, the speed of light, $c$, a mass, $\kappa$ and a length $R$.
This is defined by a non-linear extension of the Poincare algerbra, $\cal A$,
which we describe here. For $R\to \infty$, $\cal A$ becomes the Snyder
presentation of the $\kappa$-Poincare algebra, while for $\kappa \to \infty$ it
becomes the phase space algebra of a particle in deSitter spacetime. We
conjecture that the algebra is relevant for the low energy behavior of quantum
gravity, with $\kappa$ taken to be the Planck mass, for the case of a nonzero
cosmological constant $\Lambda = R^{-2}$. We study the modifications of
particle motion which follow if the algebra is taken to define the Poisson
structure of the phase space of a relativistic particle.
