In literature only very scanty information is to be found about the viscera of the Boid genera Tropidophis and Trachyboa, and therefore I believed it worth while to publish some notes which I made during dissections of the following species and subspecies: Tropidophis melanurus (Schleg.), Tropidophis maculatus haetianus (Cope), Tropidophis pardalis pardalis (Gundl.) and Trachyboa gularis Ptrs. The notes are in no way exhaustive; the specimens have been preserved in alcohol for a long time, and therefore it was not possible to study all features in detail. All but two genera of the Boidae have two well developed lungs. One of these two exceptions was mentioned already by Cope (1894, pp. 218, 220: Ungualia; 1900, p. 697), viz., the genus Ungalia (i.e., Tropidophis of present day nomenclature). In this genus only one lung is present, and besides1 a tracheal lung has developed. The second exception is the genus Trachyboa; the fact that in this genus too a tracheal lung and only one true lung have developed, seems to have escaped notice up till now. As will be shown below there are also other features in which Tropidophis and Trachyboa agree with one another, while they differ from the other Boidae. Tropidophis melanurus (Schleg.) Specimens examined: 1 $, Cuba, leg. Ramon de la Sagra, Mus. Leiden reg. no. 1299. 1 # juv., Cuba, leg. Ramon de la Sagra, Mus. Leiden reg. no. 1298. Both specimens were labelled "Ungalia maculata", but after due consideration I refer them to Tropidophis melanurus (Schleg.). Especially the identification of the male no. 1299 caused me some difficulties, and therefore I may give my reasons for this identification. This male has a quadrifurcate