526 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



matrix. The articulated left fore limb and foot was attached by 

 matrix to the string of anterior dorsal vertebrae, and to a mass of 

 thoracic ribs. Some few of the posterior vertebrae were found 

 isolated but not far removed from the articulated series. 



This specimen No. 8635, U.S.N.M., as finally assembled has the 

 following bones present: Greater portion of skuU; both rami of the 

 lower jaws; representative parts of each of the complete presacral 

 series of 27 vertebrae; first caudal; several complete and parts of 

 most of the other ribs of both sides; left scapula, coracoid, procora- 

 coid, and clavicle; left humerus, radius, ulna, and foot; left femur 

 and tibia. The vertebrae except for the loss of four centra in the 

 anterior dorsal region are quite perfectly preserved. 



The sacrum has been supplied from a second individual, No. 8661, 

 U.S.N.M., from the same deposit and of slightly smaller proportions. 

 The pelvic bones and the interclavicle were kindly furnished by the 

 late Dr. S. W. WiUiston from the collections of the Walker Museimi. 

 The right pelvic bones have the catalogue No. 8658, U.S.N.M,; 

 the left is No. 8657, U.S.N.M.; the interclavicle bears the No. 8656, 

 U.S.N.M., being the bone figured by Case in his Pelycosauria of North 

 America (pi. 15, fig. 4). The other missing parts have been restored 

 in plaster and painted a distinctive color. 



The bones were so free from distortion that it was decided to make 

 an open mount of the skeleton, though the difiiculties of domg so 

 were well understood. The imusual mechanical problems embodied in 

 the mounting of a skeleton of such fragile proportions were skillfully 

 overcome by Mr. T. J. Home, preparator in the Section of Vertebrate 

 Paleontology of the United States National Museum who mounted 

 the specimen. It is the first attempt to reconstruct a free mount of 

 an entire skeleton of a Dimetrodon, and the success of the undertak- 

 ing may be best judged by an examination of the photographic repro- 

 duction of the skeleton here shown in Plate 70. 



The pose of the skeleton was adopted after a study of living lizards 

 and is an attitude often assumed by those land forms of the present 

 day. The opening of the jaws to better display the rows of bristling 

 teeth gives the animal an appearance of angrily defying one who 

 has suddenly blocked his path. 



The specimen is standing on an artificial base colored in imitation 

 of the red clay in which the bones were originally embedded. 



Tlie total length of the skeleton from the tip of the nose to the end 

 of the tail, between perpendiculars, is 6 feet 9 inches. From the 

 base level to the top of the highest spine it measures 4 feet 9^ inches. 

 Although Dimetrodon gigos is the largest species of the genus, the 

 present individual is a moderate-sized representative of that species. 



In plate 73 is shown a model restoration of this animal prepnred 

 by the writer and which expresses his conception of its appearance 

 in life. 



