packetboat

And be it further enacted, That it shall not be lawful for any stage coach, railroad car, steamboat, packetboat, or other vehicle or vessel, nor any of the owners, managers, servants, or crews of either, which regularly perform trips at stated periods on a post route, or between two or more cities, towns, or other places, from one to the other of which the United States mail is regularly converyed under the authority of the Post-Office Department, to transport or convery, otherwise than in the mail, any letter or letters, packet or packages ofletters, or other mailable matter whatsoever, except such as may have relation to some part othe cargo of such steamboat, packetboat, or other vessel...