 Objective synonyms are common at the rank of genera, because for various reasons two genera may contain the same type species; these are objective synonyms.In many cases researchers established new generic names because they thought this was necessary or did not know that others had previously established another genus for the same group of species.An example is the genus "Pomatia" Beck, 1837, which was established for a group of terrestrial snails containing as its type species the Burgundy or Roman snail "Helix pomatia"—since "Helix pomatia" was already the type species for the genus "Helix" Linnaeus, 1758, the genus "Pomatia" was an objective synonym (and useless).