This souvenir sheet on the cover was issued in 1993 with the information that out of 75 Dutch butterfly species,15 are extinct,26 endangered and 34 species fairly common. It depicts a female Common Blue butterfly (Polyommatus icarus),which is widespread in Europe, North Africa and temperate Asia.
The 20+50c stamp on the left was issued in 1983 commemorating Johan van Oldenbarnevelt with his motto:Nil scire tutissima fides.(To know nothing is the safest creed).
Johan van Oldenbarnevelt (1547-1619) was a Dutch statesman, who played an important role in the Dutch struggle for independence from Spain.
Van Oldenbarnevelt studied law at Leuven, Bourges, Heidelberg and Padua, and traveled in France and Italy before settling in The Hague. He was a Calvinist, so he supported William the Silent in his revolt against Spain, and fought in William's army.