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We have measured photoelectron spectra for silicon cluster anions with up 50 atoms. For species with up to 20 atoms, the spectra have been compared with DFT simulations for a number of candidate low-energy $geometries.a$ An excellent agreement with experiment specific to the lowest-energy $Sin$ anion geometries (Fig. 1) validates the morphologies of medium-sized Si clusters based on the tricapped trigonal prism unit. HOMO-LUMO gaps do not decrease with increasing cluster size, but vary irregularly in the 1-2 eV range. The PES data for larger clusters with n $>25$ reveal a peculiar electronic structure for $Si33$ and $Si43$ anions. [FIGURE]