March 16 1798 datelined folded letter to Philadelphia with manuscript "Sh 24."

Rated : Sh 24 for 10 x 2 for the distance from NYC to Philadelphia + 4c Ship captain's fee. Rates calculated under the Act of February 20, 1792.

Excerpt from "The New York Clamshells and Ovals by Calvet M. Hahn":

The earliest recorded clamshell is the orange item illustrated below on a domestic letter from New York to Philadelphia with a manuscript 10c rate, dated March 10, 1798....The color of the red New York clamshells changed very early in their existence. A cover from April 9, 1798 with a manuscript Sh 14 for an incoming ship charge of 4c plus the 10c New York-Philadelphia rate is illustrated below.