A MONOGRAPH OF THE AMERICAN FROGS OF THE GENUS RANA. By G. a. Boulenger, LL.D., D.Sc, F.R.S., &c. Presented by Thomas Barbour. Received December 1, 1919. I HAVE lately been able to make a thorough revision of the numer-ous species, about 195, constituting the genus Rana in the broad sense in which I take it.^ For purposes of convenience, and also in order to facilitate its pub-lication, I have divided the work into four parts, based on the geo-graphical distribution. The first part, dealing with the South Asian, Papuan, Malanasian and Australian species, will be published, thanks to the kind interest of Dr. Annandale, in the Records of the Indian Museum, and is nearly entirely printed. The part dealing with Amer-ica, comprising a comparatively small number of species, is now offered for publication. The latest comprehensive accounts of the North American species are contained in the works of Cope, Batrachia of North America, (Bull. U. S. Nat. Mus. No. 34, 1889), and of Miss Dickerson, whose Frog Book (1906) is so excellently illustrated and swarms with inter-esting information on the life histories. The Central American species have been dealt with by Giinther in the Biologia Centrali-Americana (1900). From a systematic point of view, the descriptions in these works are not so precise and comparative as I should Avish, and do not convey that information on individual variations in the proportions that are of essential importance in a group in which the absence of scales deprives us of so many characters which facilitate the identification and study of reptiles. That is why I have thought it desirable to prepare tables of measurements of a large number of individuals to accompany the descriptions, drawn up on a strictly comparative system and taking into consideration all departures from the normal. These descriptions and tables will enable the student to form a correct idea of the material in the British Museum, material Avhich, though less exhaustive than that in some institutions in the United States, is j^et of great extent, especially as concerns IVIexico and Central America. It has been recently increased through the gener-1 Cf. Bull. Soc. Zool. France (1918), p. 111.