The Common Swift was described by Linnaeus himself in 1758 and he named the species Hirundo apus (Hirundo (Latin) = a swallow, apus (Greek) = without feet - on account of the very short legs). It was only later that it was realized that this bird was not a swallow at all but of an entirely different genus and it was renamed Apus apus. Even though the describing of species was in its infancy at that time I am quite surprised that Linnaeus made this mistake. In the hand swallows and swifts are such different birds that it should be glaringly obvious that they have to be of different genera. Even a count of the primary flight feathers would reveal this as swallows have nine and swifts ten.