Apr. 1903. North American Plesiosaurs — WlLLiSTON. 53 



for about two inches, its thickness on the margin varying from two 

 to four millimeters. Posteriorly they expand into a thickened, trian- 

 gular process on each side, projected downward and backward ovei 

 the supraoccipitals for union with the squamosals. Extending the 

 whole length of the crest is a well-marked suture. Near the anterior 

 extremity of the crest is the parietal foramen, which has been closed 

 by compression. 



The postorbital appears as a narrow bar directed outward and 

 downward. Its union with the supraorbital above and the squamosal 

 below is shown in the figure. The bone is triangular in shape, as 

 seen externally, the suture for the jugal extending back horizontally, 

 and is then turned upward at right angles to meet the free margin of 

 the arch. 



The suture separating the jugal from the squamosal begins at 

 the angle of the postorbital suture and runs obliquely downward and 

 backward to meet the lower border of the arch about fifty millimeters 

 back of the teeth. The suture is a jagged one, but its existence as 

 described and figured is beyond doubt. Professor Cope figured it 

 much further back on the arch, but his supposed suture is very plainly 

 a fracture. The bone unites below with the maxilla by a long, nearly 

 horizontal suture, that begins in an angle a little back of the middle 

 of the orbit and joins the alveolar margin near the last tooth. The 

 anterior part of the suture is nearly at right angles to the remainder, 

 joining the orbital margin back of the middle of the orbit. 



The squamosal, or squamoso-prosquamosal, is a large, triradiatt 

 bone joining the jugal and the postorbital anteriorly, the parietal 

 above, the quadrate and quadratojugal below. Cope has figured the 

 upper branch as a distinct bone under the name of supramastoid. 

 This was an error, as has already been stated. At the anterior infe- 

 rior part of the quadrate there is a distinct suture, as has been 

 figured, corresponding to the suture described as existing here in the 

 specimen of Dolichorhynchops. In the figures given of C. snovtii, it 

 was supposed that the quadratojugal was a small element. It now 

 seems probable that its relations to the squamosal are like those of 

 Dolichorhynchops; at least there is an indication that the real suture is 

 continued upward and forward for some distance. The union of the 

 squamosal and quadrate is very much as it is in Dolichorhynchops. 



The quadrate does not seem to differ from that described in Dolt' 

 cftorhynchops. 



The premaxillary is very large and massive. Its dentigerous por- 

 tion is broad and thick, with numerous pit-like depressions. It con- 

 tains six very large and powerful teeth on each side, the maxillary 



