OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 391 

 RELATIONSHIPS 



Araeoscelis is the first paleozoic reptile in which a typical upper 

 temporal vacuity has been definitely recognized. The Progano- 

 sauria, only, from an approximately . equivalent age, have been 

 accredited by Huene with a single, upper temporal vacuity, and 

 doubtless correctly, but its boundaries and position have not yet 

 been certainly determined. Inasmuch as great importance has 

 been attributed to the number and boundaries of these openings 

 in the relationships of reptiles, it will be well to discuss briefly all 

 those forms in which only an upper opening is known or supposed 

 to be present. Various theories have been proposed concerning 

 their origin and relationships, but in my opinion they are as 

 yet for the most part speculations, or at the most hypotheses. 

 Attempts to base a primary classification of the order chiefly on 

 the number of temporal openings so far have not been very success- 

 ful. The most meritorious of these attempts is that of Professor 

 Osborn, which, though it can no longer be accepted as the true 

 solution of the reptilian phylogeny, did much to place the classifica- 

 tion of reptiles on a more secure basis; notwithstanding its faults, 

 its merits are obvious. All students of the order are in practical 

 accord as regards the phyletic relationships of the double-arched 

 forms. It is only concerning those groups in which there is but 

 a single opening that grave doubt and uncertainty yet remain. 

 The single vacuity, when present, is so inconstant in its position 

 and in its boundaries that one is seldom certain whether it is the 

 upper, or lower, either or both; or, indeed, as Watson thinks, in 

 some cases neither! 



The following groups of reptiles, more generally considered to 

 be orders, have a single temporal vacuity on each side: Ichthyo- 

 sauria, Sauropterygia, "Pelycosauria," Placodontia, Therapsida, 

 Squamata and, if Huene is correct, the Proganosauria. Of these 

 the Pelycosauria and Therapsida may at once be dismissed in any 

 discussion of the relationships of Araeoscelis, since the opening, 

 whether upper or lower or neither, has such different relations and 

 boundaries as to preclude any immediate phyletic relationships. 

 And, of the others, the Sauropterygia can have only a remote rela- 

 tionship and may be dismissed from the discussion. In addition 



