AMERICAN LABYRINTHODONTIDJE 581 



between the bones are readily made out. Because B is the more 

 complete, the measurements given in the following description are 

 taken from it. 



The total length along the curve of the mandible is 495 mm . The 

 greatest breadth, 94 mm , is a little in front of the cotylus, but a breadth 

 of 90 mm or more is maintained for half the length of the ramus. 

 Thirteen millimeters from the symphysis, the most anterior part 

 where the full width is preserved, it is 65 mm broad. It is probable that 

 at the symphysis the width was not greater than 5o mm . The greatest 

 thickness is about 50™™, just in front of the cotylus, where the upper 

 part thickens abruptly. Just anterior to this the thickness decreases 

 to 2 2 mm , and remains about the same to the symphysis. The post- 

 cotyloid process is well developed. 



The articular forms the greater part of the concave cotylus, 

 and appears as a narrow ridge in the upper part of the postcotyloid 

 process. It broadens abruptly as it enters the cotylus, and is of 

 nearly uniform width to the anterior part, where it forms part of 

 the posterior boundary of the supra-meckelian foramen. The 

 greater portion of the inner side of the posterior part of the mandible 

 is formed by the prearticular. 1 It projects from the end of the 

 postcotyloid process to near the anterior end of the supra-meckelian 

 foramen. Its upper edge forms most of the inner boundary of this 

 foramen, and projects above the articular on the inner side. Its 

 lower anterior part forms the boundary of the upper posterior corner 

 of the mandibular foramen. Below it articulates with the angular 

 for most of its length. 



The angular extends the full length of the jaw on the outside, 

 but articulates with an element anterior to it about io cm from the 

 symphysis on the inside. On the inside it is narrow at the posterior 

 end, broadens gradually to the mandibular foramen, where it narrows 

 abruptly to form the part of the jaw between this foramen and the 

 lower margin. In front of the foramen it broadens again abruptly. 

 On the outside of the jaw the angular occupies about half the width 

 anterior to the cotylus, but narrows rapidly behind it. It is coarsely 

 pitted posteriorly, and ornamented with long radiating ridges and 

 furrows anteriorly. 



1 Williston, Field Columbian Museum Publication 73, Geological Series, Vol. II, 

 No. 1, p. 32; Kingsley, American Naturalist, Vol. XXIX, p. 61 (Dermarticulare) . 



