Apr. 1903. NortH AMERICAN PLESIOSAURS—WILLISTON. 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 over 
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. 3 
The suture separating the jvga/ 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 
afracture. 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 sguamosa/, or Squamoso-prosquamosal, is a large, triradiate 
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. snowiz?, it 
was supposed that the quadratojugal was a small element. It now 
seems probable that its relations to the squamosal are lke 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 guadraze does not seem to differ from that described in Dol- 
chorhynchops. 
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 
