I50 



REVISION OF THE PELYCOSAURIA. 



sented by a mere tuberosity on the edge of the rib ; the rib then curves sharply down- 

 ward again. The distal ends of the ribs are slightly expanded and round in section. 

 In the lumbar region the capitulum suddenly leaps to the edge of the centrum and 

 the tubercular tuberosity becomes a face in the same plane as the capitulum. The 

 two are closely united with the centrum and soon fuse together. The ribs were short 

 and slender and stood out nearly straight from the sides of the vertebrae. 



Fig. 65i. — Anterior surface of the clavicle ot tfie left side of A^. microdus. cl, articular lace for the cleithrum. 

 Fig. 65c. — Scapula and imperfect coracoid of the left side of N. microdus. ca, coracoid; scf, scapula. X Vi ■ 

 Fig. 65</. — Inner view of the left side of the left half of the pelvis, ilium, and pubis of N. microdus. il, ilium; 

 fii, pubis. X /3- 



The clavicle has a rounded anterior end marked by deep, radiating rugosities. 

 The posterior end is narrowed and carries strong rugosities marking the attachment 

 of the cleithrum. At the middle the bone is bent at an angle of 45° and then tapers 

 to a point. It differs from the clavicle of Dimetrodon in the corrugation of the 

 anterior edge and the sharp bend ; in Dimetrodon it is nearly straight. 



They^ri' limb is known by the humerus only, No. 4037 Am. Mus. It has the 

 general form of Dimetrodon incisivus. The articular face is oblique, but on the outer 

 edge of the proximal end is a second small face, probably marking the attachment of 

 a ligament. The bone is heavier than in Dimetrodon incisivus and the edges of the 

 articular face are marked with rugosities. Just opposite the inner edge on the posterior 

 face is a prominent nodular rugosity. The radial crest is strong and prominent, but 

 begins rather low on the proximal end. The distal end is similar to that of Dime- 

 trodon incisivus, but is stronger and roughened by rugosities around the articular faces. 

 On the lower corner of the entepicondyle is a distinct face surrounded by prominent 

 rugosities for the attachment of a ligament. 



There is a single enormous ungual phalange with this specimen, three or four 

 times as large as any occurring with the genus Dimetrodon, even D. gigas., indicating 

 enormously powerful claws on the feet. 



