habits, and behavior of the lizards of the Family Helodermatidae. New York: Bull. Amer. Mus. Natur. Hist. 109:1–238. 1956: 238. Online .pdf (页面存档备份,存于互联网档案馆)
Differential Equations from the Algebraic Standpoint by J. F. Ritt (PDF). Bull. Amer. Math. Soc. 1934, 40 (3): 197–200 [2015-05-10]. doi:10.1090/s0002-9904-1934-05808-7