From Lee Sallows:

“In his book Amusements in Mathematics, H.E. Dudeney presents a method of classifying 4×4 magic squares based on the distribution of their 8 complementary pairs 1 & 16, 2 & 15, .., 8 & 9. There are just 12 distinct such distributions or ‘graphic types’, which he labelled I to XII. The square above is an example of a type X square.”

(Thanks, Lee.)