66 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



sides terminate before the anterior and posterior borders are reached, due to the 

 wide flaring out of the edges; this flaring is especially prominent in the posterior 

 face. The transverse process rises from the neural arch and the upper part of the 

 centrum, and extends outward, backward, and downward, as in Dimetrodon. The 

 axis is decidedly Hke that of Dimetrodon, differing only in the tuberosities over 

 the posterior zygapophyses, the large size of the latter, and the size of the centantra 

 above the anterior articular face. (Compare figs. 32-35 and 58, 59, Publication 

 55, Cam. Inst. Washington.) 



The ten dorsal vertebrae, eight in connection (fig. 41 a), are from the middle or 

 posterior part of the series; they all have short, smooth spines, somewhat flattened, 

 and with the anterior-posterior diameter the longer. The base is narrowed and 

 somewhat recurved, above which the spine expands gradually to the upper end and 

 terminates in a flat face. They are easily distinguishable from the vertebrae of 

 Ophiacodon, in which the spines are less dilated and thickened above. We observe 

 no rugosity on the sides of the spines just above the base, such as occurs in 



Fig. 41. — Sphenacodon ferox Marsh, X }4. A, dorsal vertebrae; B, anterior view of a dorsal vertebra; 

 C, lateral view of same vertebra shown in fig. B. 



Dimetrodon, and which doubtless marks the attachment of the dorsal muscles 

 and the beginning of the thin cutaneous covering of the spines. The spines are 

 relatively much higher than in Ophiacodon or Theropleura. That there was 

 some variation in the height of the spines is indicated by the fact that of the 

 five vertebrae with spines attached, one, the last, has its spine notably shorter 

 than the others. 



The short transverse processes rise from the base of the neural arch and extend 

 directly outward ; the upper side of the process is thickened and convex ; the lower 

 is very narrow and does not pass obliquely downward to join the anterior border 

 of the centrum, but is set off from it sharply, indicating dichocephalic ribs. As 

 there is no face for the rib on the anterior edge of the centrum in these specimens, 

 nor any on the ends of the single dorsal intercentrum preserved, it seems probable 

 that the capitultmi artictdated, as usual, with the intercentral cartilage. The 

 sides of the centra are concave and there is a sharp median keel. The articular 

 faces are elongate, and, due to the presence of the keel, narrowed below. 



Two vertebrae (fig. 41 b, c), probably from the anterior dorsal region, have 

 much higher spines and even more prominent transverse processes than those 

 of the series of ten. These stand out almost directly from the sides of the neural 



