1050 DR. R. BROOM ON THE ORIGIN [DeC. 10,. 



what artificial group " Cotylcsauria," a view also supported by 

 Osborn (5) and Broili (9), while Boulenger (6) is inclined to place 

 the common ancestor among the Stegocephalia. Part of our 

 difficulty consists in our not knowing very clearly what a Cotylo- 

 saurian is. The term was proposed by Cope for reptiles i-e- 

 sembling Diadectes and Emjyedias, and many other forms were 

 afterwards included, for the most part very imperfectly known, 

 but supjDosed to agree with Diadectes in having the temporal 

 region roofed. Case has recently shown that in some members 

 of the Diadectidje there is a small temporal fossa, while in the 

 structure of the palate and some other points they differ greatly 

 from other known forms, such as Pariotichus, and he proposes to 

 remove them from the Cotylosauria altogether and place them in 

 another order Chelydosauria. Broili's (9) recent work on Lahido- 

 saurus shows that we have here a fairly highly organised type 

 approaching in many points the Procolophonia. Then there is 

 Fareiasaut'us, which is often also placed in the Cotylosauria, and 

 which agrees with most of the genera in having the temporal 

 region roofed, but differs markedly in a number of other points. 

 Whether it is possible to keep the Cotylosauria as a superorder 

 embracing a number of suborders which differ greatly can only 

 be satisfactorily answered when more is known of the American 

 types. In the meantime it seems better even to multiply the 

 already large number of reptilian orders or suborders than to 

 group together in an artificial manner forms that have little 

 affinity. 



As possible ancestors of the Synapsida and Diapsida we may 

 dismiss the Diadectid?e as too specialised. The Pareiasauria,. 

 while they might be considered as ancestral to the mammal-like 

 forms, are much too specialised to have been the ancestors of the 

 Diaptosaurians, even though they still seem to retain the digital 

 formula 2, 3, 4, 5, 3 *. The Pariotichidse, on the other hand, have 

 most of the characters we should want in the common ancestor 

 of the later reptiles. The few known specimens, however, have 

 lost the cleithrum which the ancestor must have had, as it is still 

 found in the Anomodonts. Fareiasa%(,rus and the Diadectids have- 

 it well developed, and it is not unlikely that forms may yet be 

 discovered resembling Pariotichus and Labidosaurus, but retaining 

 the cleithrum. Such a form might well be the looked-for 

 ancestor. 



Until recently the gap between the Therocephalians and the 

 Cotylosaurs has been a fairly wide one, but a specimen has just 

 been discovered which largely bridges it over. This is a small 

 animal found at Victoria West. It is so well preserved that, with 

 the exception of the temporal i-egion, the palate and the tarsus, 

 almost every detail of the anatomy is known. It has been named 



* There has been some difference of opinion on the digital forninla of Pareia- 

 saimis, Boulenger defiuitelj' stating that it is 2, 3, 3, 3, 3. I have elsewhei;fr 

 shown (10) that in the very closely allied Pareiasaurian genus Frojjaiipus there is. 

 reason to believe that the formula is 2, 3, 4, 5, 3. 



