96 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



The sutures of the mandible are shown in specimen No. 117 University 

 of Chicago. The bones are described as follows by Branson: 



"The sutures in the mandible of Eryops have never before been deter- 

 mined, but in all of the specimens in the Walker Museum most of them are 

 distinct. The suture between the prearticular and the splenial has not been 

 definitely located. 



"The articular is short and thick. It is covered on the outside by the 

 angular and surangular, and on the inside by the angular and prearticular. 

 The articular surface is convex, the convexity passing diagonally forward 

 from the posterior inner corner. The coronoid is very small, and is situated 

 in front of the supra-meckelian foramen, as in Anaschisma. The dentary 

 is slender, sculptured anteriorly and smooth posteriorly. The posterior end 

 of it projects a little way behind the coronoid. There is a high, thin parapet 

 on the upper side of the outer part of the bone, and the outer edges of the 

 teeth are imbedded in it. The angular forms the greater part of the outside 

 of the mandible in front of the supra-meckelian foramen. The suture be- 

 tween the angular and surangular has not been definitely determined. The 

 splenial is slender and very thin. It projects above the inner edge of the 

 dentary anteriorly, but gradually descends posteriorly. The portion in 

 front of the angular seems to be an element separate from the dentary. 

 The suture between it and the dentary appears to be near the lower edge 

 of the jaw on the outer side. As previously stated, this element seems to 

 be distinct in Anaschisma, but the evidence in neither case is conclusive. 



"The internal mandibular foramen is small, oval, situated between the 

 angular and prearticular directly below the anterior end of the supra-meck- 

 elian foramen. The supra-meckelian foramen is elongate and narrow. 



"The sculpture on the outside of the mandible consists of longitudinal 

 ridges and furrows above, but these become coarser and have more of the 

 pitted character below." 



A small skull. No. 4180 Am. Mus. Nat. Hist. Cope Coll., is possibly 

 that of a young Eryops, but, if so, the skull underwent considerable change 

 of form and proportions during development. The posterior angles do not 

 project anywhere near so far backward, not reaching beyond the extremities 

 of the tabulare; the orbits are farther back than in the adult, and the nares 

 are closer to the anterior end and more nearly strictly superior. The char- 

 acter of this skull is shown in plate 8 and fig. 26. The positions of the 

 sutures are made out from the centers of radiation of the bones, and are 

 approximate only. They differ markedly in some places from the sutures 

 drawn by Branson for the adult Eryops. 



The vertebral column: The number of presacrals is not exactly known. 

 In specimen No. 4280 Am. Mus. there are 21 counted vertebrae, but a break 

 leaves room for two or three and the first vertebra is missing, so there were 

 at least 23 or 24. Branson calculated 25 or 26 for the Chicago specimen 

 No. 117. In the specimen used for restoration. No. 4893, only 21 presacral 

 vertebrae could be placed; this is perhaps short of the normal number. 



The rhachitomous vertebrae of Eryops are well known, and the typical 

 form need not be redescribed in great detail. 



The first vertebra is represented in three specimens by the neural arch 

 alone. The pleurocentra and intercentrum being absent, the latter was 

 probably present, the former not. The neural arch consists of two halves 

 with broad faces below, in part for the occipital condyles, and slender dis- 



