Il8 REVISION OF THE PELYCOSAURIA. 



No. 4028 Am. Mus., fig. 42. Height of spine above center of neural canal, 



105 mm. 



No. 4147 Am. Mus., fig. 43 ; Nos. 4054 and 4055 Am. Mus., fig. 44. Height of 

 spine above center of neural canal, 104 mm. (This last is but a fragment among the 

 fragments of a very large and rugose skull ; it may perhaps be a specimen oi Naosait- 

 rus claviger.) 



The Ihird cervical (fig. 38) is uncrushed and shows the form without distortion. 

 The anterior and posterior zygapophyses are well developed and their articular faces 

 are decidedly oblique with a very deep pit between them just above the origin of the 

 diapophysis on the side of the neural arch. The pits of the two sides narrow the base 

 of the neural spine just above the neural canal very decidedly. The anterior face of 

 the centrum is rendered rather oval in outline by the presence of the coossified inter- 

 centrum, but the articular part proper is nearly round. The posterior face is round 

 and with wide flaring edges which are hardly recurved. 



The interceutrum is so closely united with the centrum that hardly a trace of 

 the suture remains ; the anterior portion showing on the anterior face of the centrum 

 has an upper articular portion continuous with the articular face of the centrum 

 proper, and below this a wide rather rugose portion. On the two sides of the lower 

 part of the interceutrum the two faces for the capitula of the ribs are supported on 

 prominent processes. Below, the interceutrum is continued into a sharp median keel 

 which is continuous with the median keel of the centrum. The latter is not over 

 I mm. thick and reaches to one-third the height of the centrum. The transverse pro- 

 cess is very stout ; it starts relatively far back and descends to the lower fourth of the 

 centrum. The spine is very simple. The base is thickened and somewhat elliptical 

 with the anterior and posterior ridge somewhat drawn out to an edge. Near the 

 middle of its length the shaft contracts rapidly to a nearly circular slender rod. The 

 upper end tapers abruptly and shows no face or roughening for ligamentous attachment. 

 Thsi/oicrth cervical closely resembles the first but for the more elevated spine. It 

 is not in contact with the others, so the position has been determined by its characters. 

 Following this two or three vertebrae seem to be missing. 



The dorsal vertebra-: There are eight dorsals in series and then ten which are 

 not attached, but are easily arranged from the matrix and form. The first of the 

 dorsals is evidently the first in number. The centrum is elongate vertically and 

 shortened antero-posteriorly. The lower edges of the anterior face are reverted some- 

 what on the sides of the centrum and there is a sharp median keel on the lower face 

 of the centrum, but this latter differs from Dimetrodon incisiviis, No. 146 University of 

 Chicago, and Dimetrodon giganhomogenes, No. 1 1 2 University of Chicago, in that it 

 joins the anterior and posterior edges of the centrum abruptl)- and does not gradually 

 round out before joining them. To the anterior face of the first dorsal is attached an 

 interceutrum which still shows a parapophysial facet. 



The third dorsal has the neural arch and centrum ver>' high and short. The 

 keel, which forms a straight line from the anterior to the posterior edge of the cen- 

 trum, is not over i mm. wide in its thickest part, and maintains this thickness to one- 

 third the height of the centrum ; there it suddenly expands into a rounded barrel 

 surrounding the neural canal, as shown in fig. 45. The lower fourth of the anterior 

 face is narrowed and saddle-shaped for the articulation of the large interceutrum. 

 The diapophyses are rather more close to the body of the centrum than in No. in 

 University of Chicago; they extend almost straight downward without any inclination 

 to the rear, and the lower end reaches nearly to the lower fourth of the centrum. 



