MORPHOLOGICAL REVISION OF THE SUBORDER. 



143 



Fig. 64. — The two posterior dorsal and two anterior lumbars of N. claviger. 

 No. 4015 Am. Mus. X J-J. Showing the condition of the tuber- 

 culum of the rib and the sudden change in position of the capitulum. 



process ; the ribs curve strongly backward and outward and then down. A portion 

 of the nearly complete dorsal rib has been left off in the drawing in order to reveal the 

 condition of the posterior ones. The first lumbar rib has the head suddenly shortened 



so that it extends but a short 

 distance between the vertebrae 

 and articulates largely with the 

 capitular face on the edge of the 

 centrum. In the second lumbar 

 the transverse process is very 

 sliort, hardly more than a face 

 on the neural arch ; the tubercu- 

 lum is changed from a rugosity 

 on the rib to a facet which artic- 

 ulates strongly with the face 

 for the neural arch. The capit- 

 ulum is much reduced in size 

 and articulates with the face on 

 the edge of the centrum alone. 

 The two separate sacrals are probably the first and second. Their centra are 

 nearly the same length as the last lumbars. The sacrum was strong, but the vertebrae 

 were not so firmly united as in the genus Dinietrodon. The lower edges of the centra 

 are beveled, showing that they were separated by an intercentrum instead of being 

 fused or closely pressed together with the intercentrum anchylosed below the point of 

 contact. The zygapophyses between the first and second sacrals are not over one-third 

 as large as the anterior zygapophyses of the first sacral and are poorly formed, showing 

 the degeneration due to the immobility of the 

 sacrum. The ribs are strong and closely united 

 with the vertebrae. The capitulum of the first 

 sacral rib projects slightly beyond the anterior 

 edge of the centrum to articulate with the pos- 

 terior border of the last lumbar. The rib is in- 

 clined sharply down and the distal end is flattened 

 into a vertical plate to articulate with the inner 

 surface of the ilium. The second rib is similar 

 to the first, but rather smaller. The whole dis- 

 tance across the sacrum is small, showing that 

 the pelvis was narrow as in Dimetrodoii. The 

 spines are very short and thin, but wide antero- 

 posteriorly. 



No caudals are jsreserved. 

 The shoulder girdle : This is known only 

 from isolated bones of different specimens. 



No. 4146 Am. Mus.: This is a very large 

 scapula of the left side ; the distal end and part of 

 the anterior edges are broken. It is very similar 

 in general form to that of Dimetrodon, but is 

 nearly one-third larger than Dimetrodoii dollavianits. 



Fig. 65. — Ribs of Naosaurus. a. An 

 anterior dorsal of N. microdus. 

 No. 4109 Am. Mus. All 

 others more posterior dorsal 

 ribs of A'^. claviger. No. 4002 

 Am. Mus. All X '4 ■ 



The anterior edge of the coracoid 



and procoracoid was nearly straight. The 'coracoid suture is persistent, but the 



