IN THE BEPTILIA. 23 



ly. Systematic Considerations. 



From the preceding facts certain results follow. The knowledge of the Permian 

 types enables us to trace the affinities of the orders of later ages with much more 

 precision than has been possible hitherto. In the first place, we derive the Testu- 

 dinata directly from the Cotylosauria, which realizes the theoretical type which Baur 

 correctly supposed to have given origin to all the later orders. Thus we need not 

 look for the ancestry of the Testudinata in any other group. This order then con- 

 stitutes Series I. 



As Series II we can take up the line in which the supramastoid foramen appears 

 (Ichthyopterygia). This type is not clearly marked out in the Permian, but according 

 to Baur the Triassic Mixosaurus presents an approximately terrestrial form of Ich- 

 thyosauria, which can be probably traced to Permian ancestors. This series does 

 not seem to have been continued, but this is not to be assumed, as yet, without fur- 

 ther evidence. 



As Series III we commence with the Permian Theriodonta, where an infratem- 

 poral foramen is first developed. In Diopeus a supratemporal foramen appears. The 

 latter represents the type of the Rhynchocephalia, and probably the Dinosauria, Croc- 

 odilia and Pterosauria. The loss of the supratemporal bar and preservation of the 

 zygomatic gives us the Sauropterygia. The loss of the zygomatic arch only, gives 

 us the Anomodonta ; and the non-sutural articulation of the quadrate gives us the 

 Squamata. The loss of both the supratemporal and zygomatic bars gives us such 

 Lacertilia as Heloderma and Anniella, and the Ophidia. 



The importance of the connections of the posterior bars of the skull is for the 

 first time appreciated in the present paper. It is difficult to learn these connections 

 from the writings of authors, so completely have they been neglected. For instance, 

 the terms postfrontal and postorbital are sometimes used indifferently by Marsh in 

 describing the crania of Dinosauria. It is true that in a few Lacertilia, as the 

 Yarani, these elements are fused together. The supramastoid and supratemporal ele- 

 ments have been generally confused except in the Ichthyosauria, where both exist 

 together. It may be alleged that the difference between the supramastoid and supra- 

 temporal bars is not great, and that the one might have been readily transformed into 

 the other. But this supposition will not bear examination. When the one bar has 

 been established the other has been lost, and a recovery after such loss is not proba- 

 ble. This follows from the fact that the position of a bar is the result of the loss of 

 the Cotylosaurian roof from all other regions. The only case where the reduction 

 has not at first restricted the I'oof to the position of one bar or the other, is that of 



