A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 31 



modont, this ground of ordinal distinction fails. Similarly the mode of ossification of 

 the intervertebral substance presents many types among the Anomodonts, one of which, 

 already figured by Sir Richard Owen, might be regarded as notochordal. What the 

 value of the intercentra may be I am unable to say, as they have not been figured ; but 

 intercentra, as I understand them, are not unknown among the Anomodonts. 



" The remarkable vertebral column with the elongated neural spines referred to 

 Dimetrodon is apparently unlike any known Anomodont, but the elongation of the neu- 

 ral spines in certain of the Wealden reptiles, like (?) Hylceosaurus, is not considered to 

 militate against their position in the group to which they belong. And it may be 

 doubted if the more extraordinary neural spine of Naosaurus, with its transverse 

 branches, has any greater classificational value, since the transverse branches are the only 

 characters by which the author separates Naosaurus from Dimetrodon. In Theropleura, 

 which is also described as having elevated neural spines, abdominal rods are found. In 

 a further discussion of the subject the author still considers Empedias as a member of the 

 Pelycosauria." 



In a scheme of classification given the Pelycosauria are regarded as a doubtful 

 group near to Lycosaurus and Dicynodon. 



In 1895 Seeley 45 divided the Anomodontia into three great divisions, the Thero- 

 suchia, Therochelonia and the Mesosauria or Proyanosauria. The Therosuchia is defined 

 as follows : " The palatine and the transverse bones of the palate are produced outwards 

 and usually downwards, in an arch, which abuts against the inner side of the mandible. 

 This character defines the group from the Dicynodonts, the Mesosaurs, Nothosaurs and 

 all fossil groups of rej)tiles. There are more or less completely divided heads to the dor- 

 sal ribs. A foramen of variable size occurs between the ischium and the pubis. The 

 ilium extends on both sides of the acetabulum." 



The classification here given is as follows : 



" Therosuchia comprise : 



Pareiasauria. 



Procolophonia. 

 Oorgonopsia. 

 Dinocephalia. 

 Deuterosauria. 



Placodontia. 



{Lycosauria. 

 Cynodontia. 

 Qomphodontia. 

 Endothiodontia. 



mi ( Pelycosauria. 



Iheromora -l 



I Cotylosauria. 

 Kistecephalia. 



