We describe an extension of special relativity characterized by {\it three} invariant scales, the speed of light, $c$, a mass, $��$ 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 $��$-Poincare algebra, while for $��\to \infty$ 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 $��$ taken to be the Planck mass, for the case of a nonzero cosmological constant $��= R^{-2}$. 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.

13 pages