134 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



"The mandible is rather slender, with a short symphysis, where the 

 somewhat expanded bones form a shallow but short trough, the two together 

 below gently convex from side to side. The lateral outlines of the mandibles 

 from below have a gentle concavity near the middle, curving rather strongly 

 inward behind. The inferior margin of the jaw turns upward behind rather 

 abruptly, and is narrowed from side to side. The sutures of the mandible 

 are not certainly distinguishable. Posteriorly the articular projects but 

 very little beyond the quadrate. 



" Vertebra: The axis is much broader from side to side than the following 

 vertebrae, and is very short antero-posteriorly. Its large, articular surfaces 

 fit closely the condyles of the skull. Its posterior margin below is nearly 

 parallel with the anterior. I can discover no indications of separated pleuro- 

 centra, though such may have existed. Its separated neurapophyses are 

 vertical and slender, widely separated from each other above by the massive 

 spine of the second vertebra. Above the middle of each neurapophysis 

 there is a small, posterior zygapophysis for union with the second vertebra. 

 The hypocentrum of the second vertebra is much smaller than the following 

 ones, transversely oval in shape. There may be pleurocentra here also, but 

 I can not distinguish them. The spine is very massive above, with strong 

 rugosities posteriorly, broad from side to side, with the slender neura- 

 pophyses of the axis lying in contact with it in front. The hypocentra 

 of the succeeding vertebrae are almost identical in size and shape, scarcely 

 varying a millimeter in length or breadth, though those of the sacral region 

 may be a little stouter. W here best preserved, they show a flattened surface 

 on the under side separated by a ridge from the sides, though in others this 

 flattened part seems to be merely a rounded keel. Many of the pleuro- 

 centra have been dislodged, but such as are in position in difi^erent parts of 

 the column are alike in shape and in attachment, all rather smaller than 

 the anterior or mesial ones of Eryops. The longer, neurapophysial attach- 

 ment is with the succeeding arch. These attachments of the pleurocentra 

 leave only a small surface on the hypocentrum for union with the arch, 

 which, here as in Eryops, for the most part is more closely united with the 

 pleurocentrum of the preceding vertebra than with that following the arch, 

 to which it presumably belongs. Complete spines are present in several 

 of the anterior and posterior vertebrae, but lack their distal extremities in 

 most of the others. As is the case with the hypocentra and pleurocentra, 

 they are all nearly alike throughout in thickness and length. They are a 

 little compressed from side to side, and slightly thickened at the upper 

 extremity. Anteriorly the spines are nearly vertical, but posteriorly they 

 are slightly inclined backward. The transverse processes, springing from 

 the arch, are also, so far as can be determined, nearly alike throughout the 

 presacral series. They are stout, slightly compressed vertically, and are 

 directed nearly straight outward, or a little backward. The zygapophyses 

 are rather better developed than in Eryops, and are not placed so closely 

 together, their articular facets at an angle of about forty-five degrees. The 

 transverse process for the sacral rib is very stout and heavy, with its large 

 articular facet directed outward and downward. There is but one true 

 sacral vertebra, though the transverse processes of the vertebrae immediately 

 preceding or following the sacral are heavier than elsewhere. Altogether 

 the vertebrae of Trematops are very much like those of Eryops, the pleuro- 

 centra anteriorly somewhat smaller, the transverse processes somewhat 



