Uj> FOSSIL TURTLES OF NORTH AMERICA. 



edge did not extend much below the triturating surface during life. We can not now tell 

 how wide the triturating surface was originally. At its anterior end is seen a broad articular 

 surface for the vomer. Cope thought that this surface was for the "zygomatic" bone. Cope 

 did not recognize the suture between the lower and the upper portions of the mass of bone 

 figured by him. The suture is not distinct, but the radiations on the surfaces of the bones 

 show distinctly where the suture is located. The upper bone is the prefrontal, prf. On the 

 inner side of its upper border is a broad articular surface for union partly with its fellow bone, 

 partly with the frontal. Posteriorly the prefrontal articulated with the postfrontal, pof, thus 

 excluding the frontal from the orbit. In Cope's fig. ^a is seen a bridge of bone joining the 

 prefrontal with the maxilla. The upper part of this bridge is undoubtedly the descending 

 plate of the prefrontal which joined the vomer; the lower portion of the bridge is quite certainly 

 a portion of the palatine. The foramen between the bridge and the maxilla is the nasopalatine. 

 Cope did not explain the presence of such a bridge of bone on the supposed postfrontal. 

 The bones described bv Cope as the pterygoid and the columellar, and accepted as such 

 by Baur, are the jugal, ju, and the quadratojugal, qu\. Those of the right side are shown in 

 Cope's fig. 5, plate x; those of the left side in his fig. I, plate xi. What Cope regarded as the 

 posterior end of the larger bone is the anterior. The more concave border formed a part of 

 the rim of the orbit. The form of both these bones is almost exactly as in Archelon ischyros, 

 as figured by Wieland. As in that species, the jugal extended backward to the quadrate. 

 The hinder border of the quadratojugal is concave to form the anterior boundary of the 

 tympanic cavity. It is to be noted that the conspicuous oval mark shown in Cope's fig. 1, 

 plate xi, is nothing but a little matrix overlaid by a thin layer of bone, probably of some fish. 

 In Cope's fig. 5, plate x, the quadratojugal is in nearly its natural position. It is there recog- 

 nized as the zygomatic (quadratojugal), but it is the fellow of the bone which on the other 

 side is determined as the pterygoid. The other bone, the jugal, has been turned end about, 

 to agree with Cope's idea of its proper position. 



Both quadrate bones are present; and that of the right side is represented in Cope's 

 fig. 5, plate x. Both are badly crusht, but that of the right side shows the condyle less distorted. 

 Just above the condyle, on the outside of the bone, is a scar where the quadratojugal articu- 

 lated with the quadrate. On the inner border of the latter bone is another articular surface for 

 the hinder end of the pterygoid. 



Cope's fig. 2, plate xi, represents a bone which he identifies doubtfully with the anterior end 

 of the pterygoid. It is really nearly the whole of the pterygoid, a small portion of the anterior 

 end alone being broken away. Cope's figure represents the bone as seen from below. At the 

 hinder end of the bone, on its upper surface, is a large rough surface for articulation with the 

 quadrate. From this extends forward a ridge which may have joined anteriorly either the 

 columellar bone of the lower end or the descending process of the parietal. At the hinder end 

 and below, and represented in Cope's figure, is a rough excavation for the border of the basioc- 

 cipital. The mesial half of the middle third of the lower surface is occupied by a rough surface 

 which was overlapt by the basisphenoid. The relations here appear to have been much as in 

 Dermochelys. The pterygoids are relatively narrow, outer borders thickened and obtuse. 



The bone identified by Cope as the maxilla (fig. 247, sq) is the squamosal. Cope represents 

 that of the left side. He regarded the curved border above the elongated process as the border 

 of the orbit and states that the width of the bone below the orbit was 35 mm. Fortunately, the 

 corresponding bone of the other side is present; and this shows that that curved border is the 

 result of damage to the bone. The upper edge of the bone should extend above the lower 

 border at least 90 mm. What Cope took to be the cutting-edge of the maxilla is the free, 

 sharp, and smooth hinder border of the squamosal, ascending toward the parietal. What 

 Cope regards as the premaxillarv border is a free border descending to the quadrate. The wing 

 of bone seen extending upward in Cope's figures is the horizontal plate of the squamosal which 

 overlapt the upper end of the quadrate and the outer end of the paroccipital. Pressure has 

 caused it to lie nearly parallel with the body of the bone. On the outer border, that opposite 

 the long, straight border, is seen a portion of the tympanic cavity. Wieland's figure of the skull 

 of this species shows that a process of the squamosal reaches the outer border of the parietal. 

 The true postfrontal bone (tig. 247, pof) is present, but it was not figured by Cope and 

 appears not to have been mentioned. It has on its lower border a process which articulates 



