Silver butter dishes were common in past decades, particularly in Ireland. The Irish used butter frequently as a spread and as a condiment. Butter dishes were used in order to serve butter at the dinner table.
Typically these butter dishes had the shape of a deep oval box. They typically were about seven inches long with a high cover and handle. Some antique dishes had a figure of a cow on the handle.
Value
Butter dishes are not uncommon. However antique silver butter dishes are rare and they can sell for hundreds of dollars. The value will depend on the specific butter dish. Silver plated butter dishes are not as valuable.
Sources:
The Book of Old Silver