Twelve species, six of which are new, are recorded from shores and shallow water. The most generally abundant are Spirorbis tricornigerus Rioja, S. bushi Rioja (both dextral with tube incubation), S. regalis sp. n., S. tuberculatus sp. n. (both sinistral with opercular incubation) and S. placophora sp. n. (sinistral, with tube incubation). Other sinistral species include S. claparedei Caullery & Mesnil, S. berkeleyana Rioja, S. bidentatus sp. n., and S. translucens sp. n. Dextral species include S. marioni Caullery & Mesnil, S. pagenstecheri Quatrefages and S. unicornis sp. n. The new species mentioned above have been described by the author named first. The Spirorbis fauna seems to be quite like that of Mexico and S. America, from which repeated introductions have probably occurred, perhaps on stones buoyed by seaweeds and drifting on the Peruvian and El Nino currents. Its considerable diversity is not attributed to speciation within the archipelago.
