The design is the visual features of the CONVEYOR BELT of indefinite length shown in solid lines in the drawings, whether those features are of shape, configuration, ornament, or pattern, or are a combination of any of these features. Drawings of the design are included. Figure 1 is a Top view of a conveyor belt; Figure 2 is a Left view of Figure 1; Figure 3 is a Cross-sectional view of Figure 1; Figure 4 is a Front view of Figure 1; Figure 5 is an Enlarged front view of middle ribs view of Figure 1; Figure 6 is an Enlarged side view of a lower end of a side rib view of Figure 1; Figure 7 is an Enlarged front view of a rib view of Figure 1; Figure 8 is an Enlarged side view of an upper end view of Figure 1; Figure 9 is an Enlarged cross-sectional view of a rib view of Figure 1; Figure 10 is an Enlarged cross-sectional view of middle ribs view of Figure 1; Figure 11 is a Top view of a first variant of a conveyor belt; Figure 12 is a Left view of Figure 11; Figure 13 is a Front view of Figure 11; Figure 14 is a Cross-sectional view of Figure 11; Figure 15 is an Enlarged front view of middle ribs view of Figure 11; Figure 16 is an Enlarged front view of a rib view of Figure 11; Figure 17 is an Enlarged side view of a lower end of a side rib view of Figure 11; Figure 18 is an Enlarged side view of an upper end of a side rib view of Figure 11; Figure 19 is an Enlarged cross-sectional view of a rib view of Figure 11; Figure 20 is an Enlarged cross-sectional view of middle ribs view of Figure 11; Figure 21 is a Top view of a second variant of a conveyor belt; Figure 22 is a Left view of Figure 21; Figure 23 is a Front view of Figure 21; Figure 24 is a Cross-sectional view of Figure 21; Figure 25 is an Enlarged front view of a rib view of Figure 21; Figure 26 is an Enlarged front view of middle ribs view of Figure 21; Figure 27 is an Enlarged side view of an upper end of a side rib view of Figure 21; Figure 28 is an Enlarged cross-sectional view of a rib view of Figure 21; Figure 29 is an Enlarged side view of a lower end of a side rib view of Figure 21; Figure 30 is an Enlarged cross-sectional view of middle ribs view of Figure 21; Figure 31 is a Top view of a third variant of a conveyor belt; Figure 32 is a Left view of Figure 31; Figure 33 is a Front view of Figure 31; Figure 34 is a Cross-sectional view of Figure 31; Figure 35 is an Enlarged front view of a rib view of Figure 31; Figure 36 is an Enlarged side view of an upper end of a side rib view of Figure 31; Figure 37 is an Enlarged front view of middle ribs view of Figure 31; Figure 38 is an Enlarged side view of a lower end of a side rib view of Figure 31; Figure 39 is an Enlarged cross-sectional view of middle ribs view of Figure 31; Figure 40 is an Enlarged cross-sectional view of a rib view of Figure 31; Figure 41 is a Top view of a fourth variant of a conveyor belt; Figure 42 is a Left view of Figure 41; Figure 43 is a Front view of Figure 41; Figure 44 is a Cross-sectional view of Figure 41; Figure 45 is an Enlarged front view of a rib view of Figure 41; Figure 46 is an Enlarged front view of middle ribs view of Figure 41; Figure 47 is an Enlarged side view of a lower end of a side rib view of Figure 41; Figure 48 is an Enlarged side view of an upper end of a side rib view of Figure 41; Figure 49 is an Enlarged cross-sectional view of a rib view of Figure 41; Figure 50 is an Enlarged cross-sectional view of middle ribs view of Figure 41; Figure 51 is a Top view of a fifth variant of a conveyor belt; Figure 52 is a Left view of Figure 51; Figure 53 is a Front view of Figure 51; Figure 54 is a Cross-sectional view of Figure 51; Figure 55 is an Enlarged front view of middle ribs view of Figure 51; Figure 56 is an Enlarged front view of a rib view of Figure 51; Figure 57 is an Enlarged side view of an upper end of a side rib view of Figure 51; Figure 58 is an Enlarged side view of a lower end of a middle rib view of Figure 51; Figure 59 is an Enlarged cross-sectional view of a rib view of Figure 51; Figure 60 is an Enlarged cross-sectional view of middle ribs view of Figure 51; Figure 61 is a Top view of a sixth variant of a conveyor belt; Figure 62 is a Left view of Figure 61; Figure 63 is a Front view of Figure 61; Figure 64 is a Cross-sectional view of Figure 61; Figure 65 is an Enlarged front view of a rib view of Figure 61; Figure 66 is an Enlarged front view of middle ribs view of Figure 61; Figure 67 is an Enlarged side view of a lower end of a side rib view of Figure 61; Figure 68 is an Enlarged side view of an upper end of a side rib view of Figure 61; Figure 69 is an Enlarged cross-sectional view of middle ribs view of Figure 61; Figure 70 is an Enlarged cross-sectional view of a rib view of Figure 61; Figure 71 is a Top view of a seventh variant of a conveyor belt; Figure 72 is a Left view of Figure 71; Figure 73 is a Front view of Figure 71; Figure 74 is a Cross-sectional view of Figure 71; Figure 75 is an Enlarged front view of a rib view of Figure 71; Figure 76 is an Enlarged front view of middle ribs view of Figure 71; Figure 77 is an Enlarged side view of a lower end of a side rib view of Figure 71; Figure 78 is an Enlarged side view of an upper end of a side rib view of Figure 71; Figure 79 is an Enlarged cross-sectional view of middle ribs view of Figure 71; Figure 80 is an Enlarged cross-sectional view of a rib view of Figure 71; Figure 81 is a Top view of an eighth variant of a conveyor belt; Figure 82 is a Left view of Figure 81; Figure 83 is a Cross-sectional view of Figure 81; Figure 84 is a Front view of Figure 81; Figure 85 is an Enlarged front view of a rib view of Figure 81; Figure 86 is an Enlarged front view of middle ribs view of Figure 81; Figure 87 is an Enlarged side view of a lower end of a middle rib view of Figure 81; Figure 88 is an Enlarged cross-sectional view of middle ribs view of Figure 81; Figure 89 is an Enlarged side view of an upper end of a side rib view of Figure 81; Figure 90 is an Enlarged cross-sectional view of a rib view of Figure 81; Figure 91 is a Top view of a ninth variant of a conveyor belt; Figure 92 is a Left view of Figure 91; Figure 93 is a Front view of Figure 91; Figure 94 is a Cross-sectional view of Figure 91; Figure 95 is an Enlarged front view of a rib view of Figure 91; Figure 96 is an Enlarged side view of a lower end of a middle rib view of Figure 91; Figure 97 is an Enlarged cross-sectional view of middle ribs view of Figure 91; Figure 98 is an Enlarged front view of middle ribs view of Figure 91; Figure 99 is an Enlarged side view of an upper end of a side rib view of Figure 91; Figure 100 is an Enlarged cross-sectional view of a rib view of Figure 91; Figure 101 is a Top view of a tenth variant of a conveyor belt; Figure 102 is a Left view of Figure 101; Figure 103 is a Cross-sectional view of Figure 101; Figure 104 is a Front view of Figure 101; Figure 105 is an Enlarged front view of a rib view of Figure 101; Figure 106 is an Enlarged front view of middle ribs view of Figure 101; Figure 107 is an Enlarged side view of a lower end of a side rib view of Figure 101; Figure 108 is an Enlarged cross-sectional view of a rib view of Figure 101; Figure 109 is an Enlarged cross-sectional view of middle ribs view of Figure 101; Figure 110 is an Enlarged side view of an upper end of a side rib view of Figure 101; Figure 111 is a Top view of an eleventh variant of a conveyor belt; Figure 112 is a Left view of Figure 111; Figure 113 is a Cross-sectional view of Figure 111; Figure 114 is a Front view of Figure 111; Figure 115 is an Enlarged front view of a rib view of Figure 111; Figure 116 is an Enlarged front view of middle ribs view of Figure 111; Figure 117 is an Enlarged side view of an upper end of a side rib view of Figure 111; Figure 118 is an Enlarged side view of a lower end of a middle rib view of Figure 111; Figure 119 is an Enlarged cross-sectional view of a rib view of Figure 111; Figure 120 is an Enlarged cross- sectional view of middle ribs view of Figure 111; Figure 121 is a Top view of a twelfth variant of a conveyor belt; Figure 122 is a Left view of Figure 121; Figure 123 is a Front view of Figure 121; Figure 124 is a Cross-sectional view of Figure 121; Figure 125 is an Enlarged front view of a rib view of Figure 121; Figure 126 is an Enlarged front view of middle ribs view of Figure 121; Figure 127 is an Enlarged side view of an upper end of a side rib view of Figure 121; Figure 128 is an Enlarged side view of an upper end of a side rib view of Figure 121; Figure 129 is an Enlarged cross-sectional view of middle ribs view of Figure 121; and Figure 130 is an Enlarged cross-sectional view of a rib view of Figure 121.