Sasaki, K.
1928. Serological examination of the blood-relationship between wild and domestic ducks. Jour. Dept. Agri., Kyushu Imp. Univ., 2:117-132.
Simpson, G. G.
1944. Tempo and mode in evolution. Columbia Univ. Press, New York, xviii + 237 pp., 36 figs.
Sushkin, P. P.
1924. [On the Fringillidae and allied groups.] Bull. British Ornith. Club, 45:36-39.
1925. The evening grosbeak (Hesperiphona), the only American genus of a Palaearctic group. Auk, 42:256-261, 2 figs.
Tordoff, H. B.
1954. A systematic study of the avian family Fringillidae, based on the structure of the skull. Univ. Michigan Mus. Zool. Misc. Publ. No. 81:1-42, 77 figs.
Wetmore, A.