We show that the classical Fermat quartic has exactly three smooth spatial models. As a generalization, we give a classification of smooth spatial (as well as some other) models of singular K3-surfaces of small discriminant. As a by-product, we observe a correlation (up to a certain limit) between the discriminant of a singular K3-surface and the number of lines in its models. We also construct a K3-quartic surface with 52 lines and singular points, as well as a few other examples with many lines or models. 64 [2, 0, 32] Y 56 (4, 4) 32 (3, 7) 24 64 [4, 0, 16] ?? Conjecturally, none 64 [8, 0, 8] X 56 * (4, 6) 8 (4, 4) 32 (2, 8) 16 (see page 22) X 48 (2, 8) 48 (see page 22); Mukai group F 384 75 [10, 5, 10] Q ′′′ 52 (5, 0) 4 (3, 6) 48 76 [2, 0, 38] Y ′ 52 (4, 6) 2 (4, 4) 16 (3, 5) 20 (2, 8) 14 [8, 2, 10] * Ỹ ′ 48 (3, 5) 24 (2, 8) 24 76 [4, 2, 20] Q 54 (4, 4) 24 (4, 3) 24 (0, 12) 6 ; see (D1) X ′′ 52 (6, 0) 1 (4, 4) 9 (4, 3) 18 (3, 5) 18 (0, 12) 6 ; see (D1) 79 [2, 1, 40] Y ′′ 52 (4, 5) 8 (4, 3) 12 (3, 6) 16 (2, 7) 16 [4, 1, 20] * Ỹ ′′ 48 (4, 3) 6 (3, 6) 12 (2, 7) 30 [8, 1, 10] * 80 [4, 0, 20] Z 52 (6, 0) 4 (4, 4) 12 (4, 2) 24 (2, 8) 12 ; see (D2), (D5) Z 50 * (4, 4) 10 (3, 5) 40 Z ′ 48 (4, 2) 16 (2, 8) 32 ; see (D2) Z ′′ 48 * (3, 5) 48 ; see (D2), (D5) 80 [8, 4, 12] X ′ 52 (