pointed out, especially that of Echidna. The tarsus is also more mamma- 

 lian than in any other division of reptiles. In the genus Dimetrodon the 

 coracoid is smaller than the epicoracoid, as in Monotremes. The pubis 

 has the foramen for the internal femoral artery. 



A not less remarkable characteristic of the Pelycosauria, as represented by 

 Clepsydrops and Dimetrodon, is their resemblance to the Batrachia in some 

 important respects. This is seen in the scapular and pelvic arches, which 

 resemble very much those of the Urodela, and of such types as Eryops. 

 The small coossified coracoid only differs from that of Eryops in having 

 two deep sinuses of its free border. The general form of the pelvis is 

 similar, but the ilium has a special and peculiar articular face for the sacral 

 diapophysis, which is wanting in Eryops. In the inferior arches, the ab- 

 sence of obturator fommen, and general boat-like form, are the same in 

 both ; but in the Pelycosauria the symphysis is not so deep, and the. walls 

 less massive. But the resemblance of these arches to those of the Ba- 

 trachia in question is greater than to those of any order of reptiles. 



Another point of resemblance to the Batrachia is seen in the humerus. 

 In my previous essay on the Pelycosauria above cited, I defined six types 

 of humerus as occurring in the Texas Permian. Two of these were de- 

 scribed as wanting the foramen,* while the others were stated to possess it ; 

 other differences between these types exist, but they were not mentioned. 

 Since then Gaudry has added a third form to the former group, which he 

 has ascribed to a reptile under the name of Euchirosaurus. I have detected 

 this form in my Texas collections together with another, which has no 

 condyles at either extremity. Thus eight forms of humerus are found in 

 this formation . 



That the type with the supracondylar foramen belongs to the Pelycosauria 

 has been satisfactorily shown by its presence in the skeleton of Clepsydrops 

 natalis and in Cynodraco major, where Owen first identified it. I find the 

 type without this foramen frequently associated with the skeletons of 

 Eryops, and other Stegocephali. There is no other element that can be re- 

 garded as the humerus of this type. It moreover has distinct points of 

 resemblance to the humerus of existing Batrachia, parallel with similarity 

 traceable in the femora of the extinct and recent genera. There is then 

 every reason for believing that we have in the humerus of Eryops and its 

 allies, an element which approaches closely in its characters to that of the 

 Pelycosauria, and hence to that of the Monotremata. 



There are some other peculiarities which constitute resemblances of the 

 same kind. The tooth bearing elements of the roof of the mou.h have 

 batrachian character. Such is the densely packed body of teeth seen in 

 Dimetrodon ; and so are the teeth on the vomer in Empedocles. There is 

 also a possible existence of epiphyses, judging from various specimens. of 

 humeri in my possession of both Pelycosauria and Stegocephalous forms. 



In spite of these approximations, the Pelycosauria are distinctive^' rep- 



* This word was misprinted " fossa " 1. c. p. 529. 



