The Chalon head are series of British colonial stamps during the 19th century. The name came from the painter whose portrait of Queen Victoria was re-interpreted into stamps : Alfred Edward Chalon.
New Zealand was among these colonies. Its 1855 Chalon heads were the very first stamps of this country. And that's what this 1955 stamp commémorated :
Same crown made under George IV's reign (and visible on the Penny Black and the Machin series), same youth, but different queen : Elizabeth II replaced her ancestor.