THIS plate shows the restoration of the extinct lizard, Dimetrodon gigas (Cope), lately made by Mr. Charles W. Gilmore of the United States National Museum, by whose kind permission it is here reproduced from the Proceedings of the U.S. National Museum, vol. 56, 1919. It is based upon the study of a very fine skeleton and some hundred bones of allied species, collected by Mr. Sternberg from "the Permian formation" exposed in the vicinity of Seymour, Texas, U.S.A. It is selected for illustration here because its most striking feature—the high dorsal fin-like crest along the middle of the back formed by the elongation of the neural spines of the vertebrÆ—is a puzzle to the conscientious Darwinian. Professor Case says of it: "The elongate spines were useless, so far as I can imagine, and I have been puzzling over them for several years. It is impossible to conceive of them as useful either for defence or concealment, or in any other way than as a great burden to the creatures (terrestrial non-aquatic animals) that bore them. They must have been a nuisance in getting through the vegetation, and a great drain upon the creature's vitality, both to develop them and keep them in repair." The reader is referred to pp. 127, 128, where a brief discussion of such exuberant growths will be found. The excessive growth of the median fins in the fish Pteraclis allied to the Dolphin which displays changing floods of surface colour as it dies—and in the Australian Blenny called PatÆcus—both figured on p. 130—should be compared with that of the strange crest of the grotesque Dimetrodon.