PRIMITIVE REPTILES 643 



Cleithrum well developed, vestigial or wanting; posterior 

 coraeoid bone (the so-called true coracoid bone) usually ossified, 

 its suture more persistent than that between the scapula and 

 anterior coracoid; sometimes unossified (Seymouria, Varanosau- 

 rus), a coracoid emargination, as in the Lacertilia, rarely present. 

 Pelvis with or without a median puboischiadic vacuity. 



Humerus rarely with an ectepicondylar foramen, usually with 

 an ectepicondylar groove; terminal phalanges flattened or claw- 

 like. A second centrale pedis rarely present. Articular extremi- 

 ties of long bones sometimes imperfectly ossified in the adult. 



Herbivorous (Casea) ; insectivorous (Seymouria); carnivorous 

 (Dimetrodon) ; or eaters of Crustacea, and other invertebrates 

 (Diadectes?, Pantylus, Edaphosaurus, et cetera). 



Subaquatic, littoral, cursorial or climbing reptiles. 



The above characters, both 'constant' and 'inconstant,' are 

 drawn exclusively from the American forms. To include foreign 

 forms will require some additions to the latter list: Aquatic, 

 piscivorous reptiles, with elongated neck, posterior nares and 

 other aquatic adaptations (Proganosauria) ; sclerotic plates in 

 orbits, supracoracoid foramen a notch (Paleohatteria) . 



The foregoing characters are the chief ones upon which we 

 must depend for the present at least, for the classification of 

 the known Permocarboniferous reptiles. Doubtless when we 

 shall have become more intimately familiar with the skull struc- 

 ture in more forms not a few others will be added. ^ 



These characters would seem to be ample for the separation 

 of the known genera into various orders; and they would be if 



* At the present time there is much doubt regarding the intimate structure of 

 the temporal and posterior cranial region in nearly all the genera here under dis- 

 cussion. In only the Captorhinidae of the Cotylosauria, is the controversy 

 nearly at rest. In this family {Captorhinus, Labidosaurus) it is now known that a 

 postparietal, a so-called tabulare, a squamosal and a quadratbjugal are present 

 only. The skull-structure of no single theromorph is beyond controversy. As 

 to the real homologies of the various bones of the temporal region of the reptiles 

 we are no nearer the solution than we were a score of years ago; no one really 

 knows what the homology of the mammalian squamosal is in reptiles. Eighteen 

 names — twenty if we take into consideration the different usages of supratemporal 

 and squamosal — have been applied to the four elements more usually called 'epi- 

 otic,' supratemporal, squamosal and quadratojugal, and, except for unifoi^ity 



