2 
pointed out, especially that of Hehidna. 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 archcs, which 
resemble very much those of the Urodela, and of such types as Hryops. 
The small coéssified coracoid only differs from that of Hryops 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 Hryops. In the inferior arches, the ab- 
sence of obturator feramen, 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 Butrachia 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 Huchirosaurus. 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 majur, 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 Aryops 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 denscly packed body of teeth seen in 
Dimetrodon ; and so are the tecth on the vomer in Empedocies. 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 distinctively rep- 
* This word was misprinted “ fossa” 1. ¢. p. 529, 
