No. 2300. 



SKELETON OF DIMETRODON GI0A8—GILM0RE 



535 



coracoid end somewhat inward to form the chest. The greatest 

 length of these coossified bones is 410 mm. measured over the curve. 

 Greatest expanse of distal end, 235 mm.; of proximal end, 140 mm. 



No cleithrum has been restored in the mounted skeleton as no bones 

 which could be referred to this element were found in the collection. 



The humerus of Dimetrodon gigas can only be distinguished from 

 D. incisivus by its much larger size. Case ^ observes that in the 

 humerus of the type of D. gigas " differs from Dimetrodon incisivus 

 in the articular face, which involves the whole of the proximal end, 

 and the radial crest, which, while being strong is not long, begin- 

 ning lower down on the head and not continuing so far distally. 



enl.epf. 



ec/.e/fj 



i(fr/. r. 



Fig. 6.— Left humerus of Demetbodon giqas Cope, No. 

 8635, U.S.N.M. One-third natural size. Anterior or 



VENTRAL VIEW. A., RADLAL OR DELTOID CREST; tCi. epg., 



ectepicontlar notch; ent. ep.f., entepicondylar fora- 

 men; rad. C, RADLAL CONDYLE. 



Fig. 7.— Left radius and ulna of Di- 

 metrodon gigas Cope., No. 8635 

 U.S.N.M. A. RADIUS viewed from 



THE front. B. ulna VIEWED FROM 

 the front. 0., OLECRANON PROCESS. 



Both figures one-thibd natural size. 



The edges of the proximal end are quite rugose." I fail to observe any 

 such differences. There are 16 Dimetrodon himaeri, large and small, 

 in the United States National Museum collection, and though they 

 were found to differ in some minor details all were essentially alike. 



The greatest length of the present humerus is 235 mm.; greatest 

 width of the proximal end 128 mm.; greatest width of distal end 

 136 nam.; least diameter of shaft 29 mm. 



The radius and ulna have also been carefully compared and as 

 with the humerus, their larger size is the chief difference found. 

 The principal features of these bones are shown in figures 6 and 7. 



'Publication No. 207, Carnegie Institution, Washington, 1915, p. 121. 



