EXPLANATION OF THE 

 FRONTISPIECE 



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 

 vertebrae — is a puzzle to the conscientious Darwinian. 

 Professor Case says of it : " The elongate spines were use- 

 less, 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 vegeta- 

 tion, 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 



