lOO AMERICAN PERMIAN VERTEBRATES 



the encroachment upon it of the posterior bone, the so-called true 

 coracoid, which here in this genus was so degenerate that it no 

 longer was even ossified. It seems to me that the utter absence 

 of any proof that such has been the course of evolution in the 

 pectoral girdle of reptiles — for no intermediate form has ever been 

 discovered, no form in which the posterior bone has even reached 

 as far forward as the supracoracoid foramen — is sufficient to throw 

 great doubt upon the hypothesis, a doubt that becomes quite 

 conclusive in the proof afforded by the various specimens of these 

 and other Permian reptiles. 



It is a curious fact also that a posterior coracoid bone has never 

 been observed in any temnospondyl, though the sutural division 

 between the scapula and coracoid I have observed in specimens 

 referred to Aspidosaurus to be quite as in Seymouria. 



Interclavicle (Plate IV, Figs, i, 2). — The interclavicle is shaped, 

 almost ludicrously, like a miner's shovel, with an expanded anterior 

 end and a long curved handle. The anterior end in shape is quite 

 like that of a playing card spade, thin on its margins, concave 

 above in both directions, but more so transversely. The "handle" 

 is more than three times the length of the "blade" and is of nearly 

 uniform width, somewhat narrowed anteriorly and pointed at the 

 end; its upper side is nearly flat, the imderside convex from side 

 to side. In side view the bone has a rather long and deep con- 

 cavity above to the posterior third, which is gently convex above. 

 The concavity of the upper side and convexity below are nearly 

 uniform to the extreme front end; and this shape is doubtless 

 normal, not the result of pressure, since two observed specimens 

 agree. 



Clavicles (Plate IV, Figs. 3, 4). — The two clavicles in the pres- 

 ent skeleton, as also others which have been developed, were 

 almost perfectly in place, attached to the interclavicle; and they 

 are complete save for the extreme tip, which has been lost in 

 preparation. The inner end was expanded from before back, 

 more nearly like that of Dimetrodon, a little thickened along the 

 anterior margin, quite thin on the posterior and inner sides, con- 

 cave above to fit the end of the interclavicle, with a flattened or 

 prismatic shaft, ahd so curved that it is pointed almost directly 



