Sentence:  With just the turn of a shoulder she indicated the water front, where, at the end of the dock on which they stood, lay the good ship, "Mount Vernon", river <WSD>packet</WSD>, the black smoke already pouring from her stacks. 
Meaning of the word marked with <WSD> tags:  Originally, a vessel employed by government to convey dispatches or mails; hence, a vessel employed in conveying dispatches, mails, passengers, and goods, and having fixed days of sailing; a mail boat. Packet boat, ship, vessel (Wikipedia).