Commentationes historicae : almae matri Studiorum Bononiensi novem saecula feliciter celebranti ab Universitate Iagellonica Cracoviensi oblatae. (OCLC #19366330)

RDA 3.4.5.9 on Leaves or Pages of Plates gives instructions for recording these in Extent, BUT also includes the instruction to disregard unnumbered sequences of plates unless they are substantial or referred to in a note. In most books, I see short blocks of unnumbered plates scattered throughout the book, and disregard these in RDA records.

This particular title has a block of numbered plates after the main numbered sequence, so gets

300 __ ǂa 282 pages, 31 pages of plates : ǂb illustrations ; ǂc 25 cm.

Those plates are also represented with an f in the Ills fixed field:

Ills: af__