AMERICAN LABYRINTHODONTIDM 609 



Cope says that in some specimens a groove crosses the inferior side 

 of the intercentra of the cervical region, and that the anterior part 

 is probably the hypocentrum pleurale, but he does not figure vertebrae 

 that have the groove. The pleurocentra are present in all of the verte- 

 brae excepting the atlas and axis, and possibly the posterior caudals, 

 and an examination of the specimens will convince the most skeptical 

 that they represent the same elements throughout the column. But 

 in some of the cervicals the other element, called by Cope hypocen- 

 trum pleurale, are present in the same vertebrae with the pleurocentra. 

 How, then, can the hypocentrum pleurale be the pleurocentrum, when 

 the pleurocentra are already represented in those vertebrae by other 

 elements ? The conclusion is obvious. The pleurocentra of Eryops 

 are the interdorsalia of Gadow, and not the interventralia (hypocentra 

 pleuralia), as he believes. 



Recent investigations furnish almost positive proof that the 

 homologies of the parts of Eryops vertebrae proposed by Cope are 

 correct. 



The neurapophyses (basidorsalia of Gadow) are homologous 

 with the neurapophyses of other temnospondylous Stegocephalians 

 and of the Amniota. 



The intercentra (hypocentra, basiventralia of Gadow) are homol- 

 ogous with the intercentra of other temnospondylous Stegocephalians 

 and of the Amniota. 



The pleurocentra (interventralia of Gadow) are homologous 

 with the pleurocentra (interdorsalia of Gadow) of other temno- 

 spondylous Stegocephalians and of the Amniota. 



The hypocentra pleuralia (interventralia of Gadow) are homo- 

 logous with the hypocentra pleuralia of Archegosaurus, Chelydosaurus, 

 and Sphenosaurus. 



In Archegosaurus, according to Jaekel, 1 the^hypocentra pleuralia 

 are united with the pleurocentra in the thoracic and anterior caudal 

 regions. The fate of these elements in other temnospondylous 

 Stegocephalians and in the Amniota is not known. They may be 

 united with the pleurocentra, which seems the most^probable ; they 

 may be united with the intercentra; they^mayjiave entirely disap- 

 peared; or all three of these conditions may be represented. 



1 Zeitschrijt der Deutschen geologischen Gesellschaft, 1896. 



