Round bowled soup spoons were a Victorian invention.
Sets of silverware made prior to about 1900 do not have round soup spoons; a tablespoon was used (and still is in some British houses where the silver predates 1900).
The British soup spoon is the length of a dessert spoon (i.e., smaller than a tablespoon) but with a deeper, more circular bowl for holding liquid.
The idea of including a separate soup spoon in a table setting originated in the eighteenth century, when the bowl shapes varied widely, deep or shallow, oval, pointed, egg-shaped or circular.
Spoon shapes became more standardized in nineteenth-century silverware.