41 8 S. W. WILLISTON 



lower arch with the quadra to jugal has been supposed to be lost, 

 or replaced by a ligament, and the upper bones called by various 

 names: supra temporal, squamosal, prosquamosal, etc. This lat- 

 ter view is the one now generally accepted, and, according to it, 

 the lizards have arisen from a primitively diapsid type which, by 

 the loss of the lower arch and the acquirement of streptostyly, has 

 become secondarily single-arched. Twelve years ago I ventured 

 the opinion that the two temporal bones of the squamate skull are 

 the tabular and squamosal, the former a bone unknown or unrecog- 

 nized in other reptiles since Triassic times. This view has nowhere 

 obtained approval except by Broom. For years past von Huene, 

 Broom, and I have repeatedly urged that the Lacertilia are a more 

 primitive type of reptiles than the Rhynchocephalia, and, years 

 ago, I ventured the prediction that the order would eventually 

 be discovered in the Permian. The discovery of Araeos cells in the 

 Pernio carboniferous of Texas seems to fulfil that prediction. 

 Araeoscelis has a single temporal opening bounded quite as in the 

 lizards, but with a fixed quadrate, the broad temporal region below 

 unperf orated. The cervical ribs are single-headed and attached 

 to the centra. I am convinced that the Araeoscelis type of skull, 

 by the simple emargination of the lower border of the squamosal 

 and the consequent streptostyly, gave origin to the Lacertilia. 

 Watson has also shown that Pleurosaurus, a Jurassic genus which 

 has long been located among the Rhynchocephalia, likewise has a 

 single, upper temporal vacuity, with a fixed quadrate, but the 

 squamosal narrower. He believes that the genus was ancestrally 

 related to the Squamata, though he differs from me in the inter- 

 pretation of the bones of the temporal region, adopting the original 

 Baur view of the presence of squamosal and quadratojugal. This 

 group I have called the Protorosauria, believing that Seeley was 

 correct in his original interpretation of Protorosaurus. 



Whatever may be the interpretation, one thing is evident: 

 even earlier than the origin of the upper vacuity in the Diapsida 

 a simple upper vacuity, as in the lizards, had developed, but with 

 the temporal region imperforate below, and this type persisted in 

 Pleurosaurus to late Jurassic. If the Squamata did not originate 

 in this way, then Araeoscelis and Pleurosaurus and probably 



