SYSTEMATIC REVISION OF THE SUBORDER. 43 



"The centra of the lumbar vertebrae are compressed, but not deeper than long, 

 nor acute on the median line below. The diapophyses are wide, and descend towards 

 the anterior articular border. The neural spines are compressed, and are very long. 

 Their apices are slender and are curved backwards. The faces of the zygapophyses 

 are oblique upwards and outwards. The caudal vertebree have subround articular 

 extremities anteriorly, and become more compressed posteriorly. The diapophyses 

 are median on the former, and gradually become smaller to extinction. The zyga- 

 pophyses are strong, and the neural spines continue long for a considerable part of 

 the length of the entire series. The centrum is concave below the diapophyses, and 

 has a median inferior rib. 



Measurements. 



m. m. 



Length of centrum, fourth from last lumbar ver- Depth of pelvis o.oSo 



tebra 0.018 Length of femur 120 



Vertical diameter of do 017 Long diameter of proximal end 041 



Transverse diameter of do 018 Length of tibia 085 



Elevation of neural arch and spine of last lum- Transverse width of tibia 029 



bar 087 Length of eleven caudal vertebrae 172 



( Ilium 059 Length of fourth caudal vertebra 016 



Antero-posterior extent of ] Pubis 060 Length of eleventh caudal vertebra 014 



Ischium 143 Transverse diameter of caudal 012 



"This species differs from the C. vinsloviiiw the more robust caudal vertebrae. It 

 is also considerably larger, agreeing in this respect with the C. pediinadatus. In the 

 latter the long transverse processes are decur\'ed and narrowed at the extremities in a 

 manner not seen in any of the known vertebrae of C. natalisy 



This specimen was covered with a very refractory matrix very nearly 

 the color of the bone, and only removed with great difficulty. The skull 

 was uncleaned when described by Cope, wliich accoiints for his misconcep- 

 tion of its character. The other species of this genus are indeterminate ; 

 probably some of them are good, but tbey can not be distinguished from 

 this species or from each other. Until more material is collected this will 

 remain the only determinable species. The redescription of the species 

 is contained in the redescription of the genus. 



Genus DIMETRODON Cope. 



Proc. Am. Phil. Soc, vol. xvii, 1878, p. 512 and p. 529. Also Pal. Bull. 29. 



Proc. Am. Phil. Soc, vol. xix, 1880, p. 42. 



Am. Nat., vol. xx, 1886, p. 544. 



Trans. Am. Phil. Soc, vol. xvi, 1888, p. 292. 



Type: Dimetrodon incisivus. The imperfect skull, consisting of maxillaries 

 and premaxillaries. No. 41 16 Am. Mus. Nat. Hist., Cope, coll. ; from Texas. 



Original description: "Dentition as in Clepsydrops in the superior series. 

 Pubic bone not distinct from ischium. Humerus with trochlear condyles and a 

 defined proximal articular surface. 



"The genus Dimetrodon embraces larger forms than the known species of Clep- 

 sydrops. It is probable that the species had the neural spines in the lumbar and 

 dorsal regions elevated in the same way. The humerus, while of the same general 

 character as that of Clepsydrops, differs remarkably in its more perfect articular 



