Plasmonic　nanocavity　arrays　were　achieved　by　producing　isolated　silver　semi-cylindrical　nanoshells　periodically　on　a　continuous　planar　gold　film.　Hybridization　between　localized　surface　plasmon　resonance　(LSPR)　in　the　Ag　semi-cylindrical　nanoshells　(SCNS)　and　surface　plasmon　polaritons　(SPP)　in　the　gold　film　was　observed　as　split　bonding　and　anti-bonding　resonance　modes　located　at　different　spectral　positions.　This　led　to　strong　local　field　enhancement　and　confinement　in　the　plano-concave　nanocavites.　Narrow-band　optical　extinction　with　an　amplitude　as　high　as　1.5　OD,　corresponding　to　97%　reduction　in　the　transmission,　was　achieved　in　the　visible　spectrum.　The　resonance　spectra　of　this　hybrid　device　can　be　extended　from　the　visible　to　the　near　infrared　by　adjusting　the　structural　parameters.