The arrest follows a police release of a photo after two incidents on the No 3 bus route, one on June 29 in Gossops Green and one in Pound Hill on July 2, police added. Sussex Police said neither of the girls were harmed and were able to leave the buses safely.
As a result of information received following a public appeal on July 26, and other enquiries, officers arrested a 24-year-old man the next day on suspicion of outraging public indecency.
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After being interviewed, Sussex Police said he was released on bail with conditions until August 24 while enquiries continue.
Detective Inspector Ali Hutchings said: "Anyone who has any other information, is asked to report online or call 101, quoting serial 1093 of 29/06."
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111.