68 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



brse, apparently in a connected series, a few caudal vertebra;, and an incomplete femur. 

 Figures of many of these bones, carefully made by Williston, are given in figs. 4-'-45 and will 

 render an extended description unnecessary. The vertebral spines, it will be seen, are all 

 of nearly uniform length, though they shorten somewhat toward the axis; they are dilated 

 and thickened above, rounded and stout below. On a number of the posterior ones 

 (fig. 43 A, B, c) there is a facet, it will be observed, for the capitulum, an unusual thing in 

 the Pelycosauria. The axis agrees with the specimen previously described. The nearly 

 complete innominate bone (fig. 43 d) is indistinguishable from that of Dimetrodon. 

 The scapula (fig. 44 a) shows only minor differences in comparison with an unusually 

 well-preserved scapula of Dimetrodon, collected by Mr. Hatcher on Coffee Creek, Texas, and 

 preserved among the Yale collections (fig. 44 b). The sutural lines between the scapula 

 and coracoids are shown very clearly in both specimens. In the specimen of Sphenacodon 

 the preglenoid facet is imperfect. The humerus (fig. 45 a) also shows an amazing resem- 



FiG. 43. sphenacodon ferox Marsh, No. 818, Yale University, X % A, B, C, lateral view of three 

 posterior dorsal vertebras; D, right innominate bone. 



blance to that of Dimetrodon* The femur of this specimen is imperfect; a perfect femur 

 from another specimen, agreeing well with this incomplete one, except that it is slightly 

 smaller, is shown in fig. 45 b. 



The sacrum is quite that of Dimetrodon, so far as the incomplete specimens show; it 

 has three vertebrae. The parts of the sktdl of this and other specimens in the Yale col- 

 lection indistinguishable from it agree very well with the ones referred to the type speci- 

 men, except in size. 



As has been stated, there seem to be minor differences in the length and characters of 

 the spines among the material in the Yale and Chicago collections that might indicate 

 specific variations. Possibly, when the complete anatomy of the genus is known, as in 

 Ophiacodon, these differences may justify its separation into two or more closely allied 

 genera. The size, typically, is smaller, and no such broad-ended spines as those figured 

 herewith as belonging with specimen No. 818 of the Yale collection have been discovered 

 in the Baldwin quarry, whence came the holotype specimen of Marsh; though on the other 

 hand, this collection does contain spines too long for Ophiacodon, though thinned above. 

 But these details are unimportant at the present time. The one thing now absolutely 



* It was chiefly on this humerus, together with the incompletely prepared spines of this specimen, 

 that I reported in an earlier paper the occurrence of Dimetrodon in the New Mexican fauna. As a fact, 

 there is not a single specimen in either collection which can now be referred with any probability to the 

 genus Dimetrodon. I think it may be definitely said that the genus does not occur in New Mexico. 



