Kaplansky and Riordan have unified and generalized various results in statistics, in terms of Problem of Rooks, on a trapezoidal chessboard. A key theorem is: the number of ways of putting c non-attacking rooks on a right-angled isosceles triangle of side r-l is Stirling number Ar-c Or/(r-c)!= rcQr. In other words, this is number of selections of c points on such a board, such that none have any row or column index in common. [1] We will exhibit well-ordered tables of these point sets thru r = 5, in l to I correspondence with sequations (rhyme schemes) also enumerated by Stirling numbers [2,31. We will then formulate other classifications, with respect to: 2) row location of topmost rook; 3) number of rooks on principal diagonal; 4) column vacancies; 5) column location of bottom rook. Each of these except 3), of course has a dual interpretation, under interchange of row and column. In Table I, row index precedes column index, and a vacant board is indicated by 0. The index 11 is at top of board, away from observer, with rr at bottom diagonal corner nearby on right. The sequations have further isomorphs in substitution cycles [4]. All rhyme repetitions of kth letter correspond to all letters in kth substitution cycle. ITus sequation aaaaa corresponds to distribution or substitution cycle (abcde), while sequation abcde corresponds to distribution a/b/c/dJe, etc. These correspondences are too easily read off by inspection, to need printing here.