Nilokeras I, Alander, Hyblaeus,| | Lethes, Amenthes, Thoth, | | Sitacus, Astaboras, Vexillum, | | Phison, Euphrates, Hiddekel, | | Adamas, Eunostos, Aethiops, | | Gelbes, Avernus N, Naarmalcha, | | Is | 17 | 23 | | Between 30° N. and 40° N. Deuteronilus, Alander, Nar, | | Marsias, Fretum Anian, | | Amenthes, Thoth, Vexillum, | | Phison, Euphrates, Hiddekel, | | Adamas, Eunostos, Djihoun, | | Gihon, Nilokeras I, Chaos, | | Gelbes, Aethiops, Naarmalcha | 12 | 20 | | Between 40° N. and 50° N. Fretum Anian, Pyramus, | | Protonilus, Propontis[4] | 3 | 4 | | Between 50° N. and 60° N. Callirrhoe, Fretum Anian, | 3 | 3 Pierius | | | | Between 60° N. and 63° N. Pierius, Callirrhoe | 2 | 2 ===========================================================+=====+===== From this tabulating of them it is apparent that the doubles are practically confined to the zones within forty degrees of the equator. Only 7% of them straggle farther north than this, while above 63° north latitude and 35° south latitude there are none. Such a distribution is not in proportion to the areas of the zones, which though diminishing toward the poles do so at no such rate. The surface included between the equator and 40° of latitude is 65% of the hemisphere, whereas the fraction of the number of doubles found there is 93%. The doubles are, then, an equatorial feature of the planet, confined to the tropic and temperate belts.