94 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



frontals, nasals, and lachrymals. They meet, or very nearly meet, the postfrontals 

 behind, so that the frontals take little if any part in the upper edge of the orbit. 



The frontals reach nearly or quite from orbit to orbit and extend an equal 

 distance anterior and posterior to them. This portion of the skull is flat or slightly 



concsvc. 



The parietals are wide, extending beyond the frontals; the parietal foramen 

 lies in the anterior third. The posterior edge of the parietal is separated from the 

 posterior border of the skull by the upper edge of the vertical supraoccipital plates. 



The postfrontals are small triangular bones, forming the posterior half of the 

 upper edge of the orbits and a part of the posterior edge. 



The postorbitals are nearly square; they form the greater portion of the pos- 

 terior edge of the orbit. 



The ju?al is elongate, extending from the anterior edge of the orbit almost to 

 the posterior end of the skull. It is quite high in the middle, and forms with the 

 postorbital the posterior rim of the orbit. 



The squamosals: On either side of the parietal are two bones which form the 

 posterior part of the temporal roof. The upper of these, occupying the position of 

 the squamosal, is rather longer than broad and extends as far forwards as the pane- 



FiG.40— a. Upper view of skull of Captorhinus isolomns. X |. No. 4338 Am. Mus. Lettering as in 

 b. Upper view of skull of C. aguti. X J. No. 4334 Am. Mus. 

 f. Upper view of skull of C.aguti. X jj. No. 4338 Am. Mus. 



59- 



tal foramen. Below this is a larger bone which articulates with the postfrontal, 

 postorbital, and jugal; its posterior edge forms the edge of the skull and covers the 

 quadrate; it is regarded as the prosquamosal for the following reasons: 



The posterior surface (fig. 39, c) of the skull is formed above by a pair of plates 

 on either side, lying at right angles to the bones of the surface. The inner bones are 

 the supraoccipital plates; they meet in the median line and extend downward, 

 probably forming the upper edge of the foramen magnum. The outer end termin- 

 ates in a point which is wedged in between the squamosal and the second plate on the 

 posterior surface. This plate is abruptly wider than the supraoccipital and extends 

 down to the posterior angle of the skull, completely covering the quadrate behind. 

 Between the exoccipital and the second plates on each side is the large posttemporal 

 fenestra. The outer pair of plates is homologous with the bone identified in the 

 Pelycosaurs as the quadratojugal. 



A small triangular element lying between the supraoccipital plate, the squa- 

 mosal, and the quadratojugal is the last trace of the tabulate, as suggested by Cope. 



With the recognition that the temporal region is covered in the Diadectida, 

 Pariotichidce, and Captorhinidce by only two elements instead of three, as in the 



