640 S. W. WILLISTON 



era from Illinois, Kansas, Oklahoma, Texas, New Mexico and 

 Colorado. And I need not add that I have diligently studied 

 all the literature bearing on these American reptiles, especially 

 that of Case and Broili. I am indebted to Dr. Case for the 

 kindly criticism of the manuscript of the present article. 



It will be understood that I give the characters so far as they 

 seem to be established by numerous forms, though it is quite 

 possible that future discoveries of new forms, or of better material 

 of forms now imperfectly known, may require the removal of 

 some of the characters included under the constant list to the 

 inconstant or variable list. But the converse will not be 

 possible unless I have committed errors, since here the evidence 

 is positive, not negative. Among so many and diverse forms 

 it must be evident that most of the characters common to all, 

 so far as the material goes, are to be considered as primitive 

 ones, that is, characters possessed by the earlier or earliest rep- 

 tiles far back in Pennsylvania times. But, by no means are 

 these the only primitive characters, since it is very evident that 

 even by the close of the carboniferous not a few had become 

 variable. 



CONSTANT CHARACTERS OF PERMOCARBONIFEROUS REPTILES 



Crawling reptiles from about 0.3 to about 2^ meters in length. 

 A parietal foramen, postorbital, postfrontal, lacrimal, nasal and 

 probably at least one additional membranous cranial bone not 

 occurring in Sphenodon present in the skull. Quadratojugal, 

 paroccipital, epipterygoid and septomaxillary probably always 

 distinct; parietals, frontals and nasals never fused in middle 

 line; stapes probably always large; a separate prearticulai-^ bone; 

 splenial entering symphysis; coronoid small; teeth on paired 

 premaxillae, maxillae, palatines, pterygoids and dentaries; ptery- 

 goids articulating with vomers (prevomers), basisphenoid, pala- 

 tines and quadrates; quadrate always fixed, though not always 

 firmly attached. 



' This term (1903) had become established in paleontological literature before 

 (iaupp ('08), in ignorance of its use, proposed the name goniale for the same bone. 



