The differences in the length of the exposed culmen of these terns shows that birds from islands more remotely oceanic possess longer bills than do those from islands closer to the Asiatic continent. Murphy (1938:538) has written that this phenomenon is characteristic among some species which have both continental and insular populations (or subspecies). Figure 10 shows the southeastern part of the range of the subspecies, _Sterna s. sumatrana_, and gives the average measurements of the exposed culmen of birds from several localities. These localities are given in table 19. Terns with longer bills (37-39) were taken in Micronesia, in the Polynesian islands, and in northern Australia. Terns with shorter bills (34-36) were taken in Melanesia, Malaysia, and the coastal region of China, but there appears to be no abrupt line of demarkation between them. Further evidence of this tendency may be obtained from the literature. Kuroda (1925:191) gives the measurements of the exposed culmen of seven males and five females from the Riu Kius as averaging 35 mm. (range 31-40.5). It is also of interest to note that the length of the exposed culmen of the males averages one to two mm. longer than that of the females. The status of _Sterna sumatrana mathewsi_ may be questioned. I find no characters separating my series of mostly poor specimens. The systematic position of this subspecies from the Indian Ocean (and likewise the status of subspecies of other sea birds which range into the Indian Ocean) may not be known with certainty until additional material is obtained. [Illustration: FIG. 10. Geographic variation in the average length of the exposed culmen of _Sterna sumatrana sumatrana_.] =Sterna lunata= Peale Spectacled Tern _Sterna lunata_ Peale, U. S. Expl. Exped., 8, 1848, p. 277. (Type locality, Vincennes Island, Paumotu Group.) _Sterna lunata_ Hartlaub, Proc. Zool. Soc. London, 1867 (1868), p. 831 (Pelew); Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 9, 118 (Pelew); _idem_, Proc. Zool. Soc. London, 1872, pp. 90, 113 (Pelew); Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 5, 41 (Palau); Saunders, Cat. Birds British Mus., 25, 1896, p. 100 (Pelew); Takatsukasa and Kuroda, 1, 1915, p. 62 (Ruk, Pelew); Hand-list Japanese Birds, rev., 1932, p. 195 (Palau); Hand-list Japanese Birds, 3d ed., 1942, p. 218 (Palau); Mayr, Birds Southwest Pacific, 1945, p. 26 (Micronesia). _Onychoprion lunatus_ Salvadori, Ornith. Papuasia, 3, 1882, p. 451 (Pelew); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 76 (Pelew). _Melanosterna lunata_ Kuroda, in Momiyama, Birds Micronesia, 1922, p. 52 (Pelew). _Geographic range._--Breeds in Oceania from the Hawaiian Group south to Fiji and the Tuamotus and west to the Moluccas. In Micronesia: Palau Islands--exact locality not known.