Longacre's design was based on his two-cent pieces, and symbolizes the strength of a unified America. The nickel proved difficult to strike and the reverse, or tails, design was modified in 1867. Even so, production difficulties continued, causing many minor varieties which are collected today. Minting of the Shield nickel for circulation was suspended in 1876 for a period of over two years due to a glut of low-denomination coinage and it was struck in only small quantities until 1882. The following year, the coin was replaced by Charles E. Barber's Liberty head design.