154 



REVISION OF THE PELYCOSAURIA. 



The stapes: On either side of the basisphenoid is a short, wide bone, which 

 occupies the position of a stapes. The inner end is smaller, but terminates in a flat 

 surface ; just below the extremity the bone is pierced by a foramen. 



The palate is well preserved on one side. There is a great median vacuity form- 

 ing the posterior nares, but there are no palatal vacuities. The sutures between 

 the pterj-goids, palatines and prevomers can not be made out. 



The prevomers are thin plates 

 connecting anteriorly and laterally 

 with the premaxillaries and anter- 

 iorly with each other; more pos- 

 teriorly they are cut out on the 

 median line, so that when the two 

 were in position there was an elon- 

 gate heart-shaped vacuity in the 

 Fig. 70.— Diagram of the upper surface of the lower jaw of Edapho- median line. At the anterior end, 

 saurm pogonias. where the two boues meet, there are 



four conical teeth on each bone ; the posterior is the larger. 



The pterygoids articulate with the basisphenoid in the mid-line and send a strong 

 process backward, which articulates with the inner side of the lower end of the quad- 

 rate. There is no descending external process forming a buttress for the lower jaw, 

 as in the other Pclycosaiiria. The line of union with the palatine can not be made out. 

 Covering a large portion of the pterygoid and the palatine is an oval plate studded 

 thickly with stumpy conical teeth irregular>' arranged. On the inner edge there are 

 some teeth of smaller size. Most of the teeth are injured by decay, but it can be seen 

 that the ends were very blunt, resembling the pharyngeal teeth of Labrus. The plate 

 bearing the teeth is very heavy and extends backwards, underlying the anterior half 

 of the temporal region. 



The hnver jaw of the left side is nearly perfectly pre- 

 served. The sutures between the separate bones can not 

 be made out. The anterior symphysis is very strong and 

 was formed by the splenial as well as the dentary. There 

 are twenty counted teeth and alveoli and there were per- 

 haps three or four more at the posterior end. The anterior 

 teeth are similar to the premaxillary teeth above, but there 

 are none corresponding to the triangular teeth of the an- 

 terior portion of the maxillary — all are conical, growing 

 smaller towards the posterior end. The ah-eolar edge is 

 somewhat elevated. In the posterior half of the jaw is a 

 dentigerous plate corresponding in size and shape to the 

 pterygoid plate above and studded with the same kind of 

 teeth. It is probably supported largely by the dentary, but 

 the splenial may also take part. The articular region has 

 two cotyli corresponding to the condyles of the quadrate above. There are no open- 

 ings on the outer side of the jaw and none can be made out on the inner side. 



The axis has a short centnnn with elongate pits on either side as in Naosaitrus. 

 The transverse processes rise from the neural arch and the upper edge of the centrum; 



Fig. 7i. — Axis of Edaphosaurus 

 pogonias. 



