A MOUNTED SKELETON OF DIMETRODON GIGAS IN THE UNITED STATES NATIONAL MUSEUM, WITH NOTES ON THE SKELETAL ANATOMY. By Charles W. Gilmore, Associate Curator, Division of Paleontology, United States National Museum. INTRODUCTION. During the spring of 1917 the United States National Museum ac-quired from Mr. C. H. Sternberg, a small collection of vertebrate fossils, which he and his son Levi had made earlier in the season from the Permian formation as exposed in the vicinity of Seymour, Baylor County, Texas. The collection consists of a very fine skeleton of Dimetrodon gigas Cope, several hmidred bones of the smaller species of Dimetrodon, and between 35 and 40 skulls and partial skeletons of the smaller reptilian and batrachian forms that comprise this interesting fauna. The greater part of the collection was obtained from a deposit of bones on the Craddock ranch, discovered in 1909 by members of an expedition from the University of Chicago. In writing of this dis-covery. Doctor WiUiston ^ designated it as the "Craddock Bone Bed," and I quote below from his remarks on the manner of occur-rence of the fossils found there. The bones in tliis deposit extend through a thickness of about 1 foot over a con-siderable space, a few hundred square feet, imbedded in red clay like that of the Cacops bed. They are unlike those of the Cacops bed, however, for the most part isolated and generally more or less free from incrusting matrix, and usually in the most perfect preservation. Not a few, however, show effects of erosion, as though they had been rolled upon a beach of hard, shallow bottom. The skeleton of Dimetrodon gigas, as so often happens in deposits of fossil bones, was the one exception to the general conditions pre-vailing there in that considerable portions of the skeleton were found articulated, and the association of these articulated and other parts as pertainuig to a single individual was further indicated by an adhering matrix which cemented them together into compact masses. For example, the skull was found disarticulated, but its separate ele-ments with the jaws were bound into one mass by the enclosing 1 Williston, S. W., American Permian Vertebrates, pp. 5-7, 1911. Proceedings U. S, National Museum, Vol. 56— No. 2300. 525
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