This is Scott #14, 10c green type II Washington 10c stamp of 1855. Type II means that the engraved lines are complete above the two "X"s at the top of the design. At the bottom of the design, the outer line below the label "Ten Cents" is broken in the middle, and the shells at the bottom are partly cut away.

Surprisingly these classics have not gone way up in price like many US coins of the 19th century. This one came with a 1984 certificate from the
Philatelic Foundation, attesting to its authenticity.
