The irregular distribution of _D. oceanica_ in the islands of Micronesia and the fact that the bird exists on both "high" volcanic islands as well as on "low" coral atolls suggest that the present population may be a remnant of a once more widely distributed one. The fact that _D. oceanica_ may be divided into several subspecies shows that a greater amount of geographic variation has occurred as compared with its probable ancestral stock, _D. pacifica_, which is virtually undifferentiated over most of its extensive range. The pigeon of Micronesia has a more rounded wing than that of _D. pacifica_, which might, as Amadon has suggested, cause the bird to be more sedentary and lend itself more readily to differentiation through geographic isolation. _D. pacifica_ is known to fly from island to island. As shown by the measurements in table 27, the length of wing of _D. oceanica_ differs, in the various insular populations, being longer in the west and shorter in the east. This cline has been discussed by Amadon (1943:11). It is interesting that _Ducula_ or some other large pigeon has not become established in the Mariana Islands. _Ducula_ is present at Yap and Truk, which are not very distant from Guam. Another tropical pigeon, _Columba vitiensis_, has extended its range northward and reached the Bonin Islands; probably it arrived there via the Philippines or the Riu Kiu Islands. Thus, there are representatives of large pigeons on islands to the southeast, south, west and northwest of the Marianas, but none has become established in the Marianas themselves. =Streptopelia bitorquata dusumieri= (Temminck) Philippine Turtle Dove _Columba dusumieri_ Temminck, Pl. col., livr. 32, 1832, p. 188. (Type locality, Vicinity of Manila, Luzon, Philippine Islands.) _Colombe Dussumier_ Quoy and Gaimard, Voy. "Uranie," Zool., 1824, pp. 35, 680 (Mariannes); _idem_, Ann. Sci. Nat. Paris, 6, 1825, p. 148 (Mariannes). _Columba dusumieri_ Wagler, Syst. Avium Columba, 1827, p. 266, sp. 99 (Marianis). _Columba Dussumieri_ Kittlitz, Obser. Zool., in Lutké, Voy. "Le Séniavine," 3, 1836, p. 305 (Guahan). _Streptopelia gaimardi_ Bonaparte, Consp. Avium, 2, 1854, p. 66 (Type locality, Mariannes); _idem_, Comptes Rendus Acad. Sci. Paris, 40, 1855, p. 18 (Mariannes); Reichenbach, Tauben, 1862, p. 76 (Mariannen). _Turtur (Streptopelia) Giamardi_ Gray, Cat. Birds Trop. Is. Pacific Ocean, 1859, p. 43 (Guam). _Turtur gaimardi_ Gray, Hand-list Birds, 2, 1870, p. 239 (Marian).