46 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



are conspicuously different from those immediately adjacent, as shown in the 

 figures; so different, indeed, are these spines that had they been found isolated 

 they would have been unhesitatingly referred to a different genus from that of the 

 other vertebras. Doubtless they are anomalies that will not be found in other 

 specimens of the same species. 



The diapophyses are very much as they are in Varanosaums * and Dimetro- 

 don. Those of the cervical region are stouter, and are directed outward, downward, 

 and backward, becoming almost transverse in position in the sixth, quite as in Vara- 

 nosaurus. Beginning with the seventh vertebra the processes project transversely, 

 gradually becoming shorter and less stout, until in the last, that is, the first presacral, 

 they are mere tubercles for the sutural attachment of very short ribs. In all the 

 presacral vertebrse, unless the first three are exceptions, the articular surface for the 

 tuberculum is continuous on a thin prolongation extending downward and forward 

 to the intercentral space. The diapophyses are located exclusively upon the arch, 

 as shown by distinct sutural lines distinguishing the arch from the centrum. 



Fig. 26. — Ophiacodon mirus Marsh, X yi- A, twenty-first to the twenty-sixth vertebrae 

 from the side; B, first presacral, sacral, and two proximal caudal vertebras from the side. 



The intercentra were probably preserved throughout the presacral series, but 

 a few have been lost in the preparation of the specimen. They measure about 

 12 mm. from side to side and 4 mm. in width. 



Sacrum: Unfortunately, as already explained, the sacrum of the more perfect 

 specimen (No. 650) was lost in collection. Of the second specimen (No. 651) the 

 posterior presacral vertebras, the sacrum, and numerous vertebrse of the tail were 

 found loosely united by matrix, though with their processes more or less broken 

 away and lost. The sacral vertebrse, so far as they are preserved, scarcely differ 

 from those immediately preceding, except in their ribs and rib attachments. The 

 sutural surfaces for the ribs, shown fully on the right side, are very extensive, 

 especially in the first of the two vertebra. The diapophysial surface is broad and 

 overhanging; the parapophysial surface, of less extent, reaches quite to the lower 

 margin of the centrum at the anterior end. On the second vertebra the surfaces 

 are less extensive, about equally divided between arch and centrum, and the ribs 

 of both vertebras projected at their capitular end into the intercentral space. The 

 distal extremities of the sacral ribs of both vertebras are lost, but a nearly complete 

 rib found among the loose bones in the wash shows a structure not unlike that 

 of Varanosaurus. There were but two pairs of sacral ribs, as shown in the figure. 



Caudal vertebra: With the more complete specimen thirteen vertebrae were 

 found associated, connected by matrix in two series, as shown in fig. 27. From 



* Williston, American Permian Vertebrates, plates i, ii. 



