408 The American Naturalist. [May, 



of the roof. The existence of the genera of Cotylosauria in America 

 and South Africa (Pariasaurus Owen), in the Permian beds, gives 

 probability to such a theory, and I selected the genus Pantylua which 

 presents the most unmodified type, as serving best as a basis of com- 

 parison for other orders of Keptilia. The segments concerned are the 

 postfrontal, postorbital and jugal in front; and the supramastoid, 

 supratemporal, and zygomatic, as the posterior elements of the roof 

 and its resultant arches. The name zygomatic was employed for the 

 element often called quadratojugal ; supratemporal for the so-called 

 squamosal ; and supramastoid for the mastoid of Cuvier, a name 

 already given by Cuvier to a distinct region of the mammalian 

 skull. 



I showed that the modifications of the Cotylosaurian roof, fall into 

 the following categories. 



1. "Roof reduced at margins only." (Baur). 

 One arch remaining (postorbital-supratemporal) in 



reduced types ; or none ; Teskdinata. 



2. One perforation only ; no marginal reduction. 

 Perforation superior, not interrupting postfronto- 



supramastoid connection ; Ichthyopterygia. 



Perforation superior, interrupting postfronto-supra- 



mastoid connection ; Pseudosuchia. 



Perforation inferior, not interrupting postfrontal 



or postorbital connections ; Pelycosauna. 



Perforation extensive, preserving only the jugal- 



3. Two perforations; no marginal reduction. 

 Postfrontal supramastoid connection interrupted; Bhynchocepha, 

 Postfrontal and postorbital elements fused ; Dinosaw 



4. One foramen and inferior reduction by loss of 

 zygomatic arch. 

 Quadrate bone fixed by suture ; AnomodonUa. 



Quadrate not fixed by suture ; Squamat* 



The clearing up of the homologies of the arches is necess 

 correct understanding of the relations of the members of the Rep* ia - 



Five plates illustrate the memoir, of which three ar. 

 duced, copied from the Transactions of the American I Inlosop 

 Society.— E. D. Cope. 



