268 S. W. WILLISTON NEW GENERA OF PERMIAN VERTEBRATES 



in the reptilia was articulated invariably with the intercentrnm and 

 neurocentrum, and never with the centrum exclusively. In the rhachito- 

 mous amphibia the articulation as seen in the present form was with 

 hypocentrum and neurocentrum. Probably that was the invariable rule, 

 for I know of no amphibian in which the capitulum of the rib articulated 

 between the centra. This fact is suggestive, at least. 



Yet, further, in the embolomerous forms it is the pleurocentra which 

 become detached from the remainder of the vertebra to form an inde- 

 pendent disk between the hypocentra, just as is the case in the atlas of 

 the amniota. 



I am fully conscious that the theory of the hypocentral origin of the 

 centra of modern amphibians and the exclusively pleurocentral origin of 

 the same of the amniota seems a bit improbable, though, of course, not 

 impossible ; I am not ready to receive it as a safe theory yet ; I am still 

 less ready to accept the theory of the independence of intercentra and 

 hypocentra morphologically, as the other theory demands. 



On a later page of this article I give the description and figures of a 

 remarkably amphibia-like reptile, in which the vertebral structure seems 

 to be intermediate between the rhachitomous and the reptilian type. It 

 is not decisive, but is very suggestive. 



PECTORAL GIRDLE AND EXTREMITY 



Scapula coracoid. — The scapula coracoid (plate 10, figure 1 ; plate 11, 

 figure 1 ) is a relatively large bone, with no indications of sutural division 

 into its supposed component parts. The blade is moderately expanded 

 above, gently concave on its outer, convex on its inner, surface. Its upper 

 border is a little convex longitudinally, its edges sharply truncate for 

 cartilage. The posterior border is thickened to the beginning of the 

 glenoid concavity ; the corresponding anterior border is thinned. 



The posterior border divides to include the supraglenoid fossa, per- 

 forated at its bottom by the supraglenoid foramen. The outer border 

 continues downward, and by a gentle curve backward to terminate in the 

 oval preglenoid facet, which looks downward, backward, and outward. 

 The inner margin, the thicker, extends downward, inward, and back- 

 ward, with an anterior curvature. In one specimen the end is angularly 

 truncate, in all probability for a small metacoracoid that was not ossified. 

 In the others it continues in a thin border back of the margin of the 

 posterior glenoid facet. This latter facet is near the lower part of the 

 bone, an elongate concave surface, with sharp margins posteriorly, and is 

 opposed to the anterior facet already described. Between these two facets 

 and a little above them the glenoid foramen pierces the bone obliquely 



