APR. 1903. NortTH AMERICAN PLESIOSAURS—WILLISTON. 17 
formed by the ‘“‘frontals”’ is stout and rounded, and is continued at 
least as far forward as the anterior end of the orbit, clearly separated 
above and below by the median suture. The anterior ends are lost in 
front in the broken fragments of bone, between and beyond the 
anterior end of the orbits. Lying between the orbits, and separated 
from each other by a narrow interval, are the narrow bones which may 
represent the conjoined postfrontals and prefrontals and nasals. On 
the right side, as stated above, the bone had been macerated away, 
and while some of its processes had been broken off and lost, the 
sutures for union with the parietal, frontal and prefrontal are beauti- 
fully preserved, showing the relation to these bones in a way that 
precludes-doubt. The bone shows no trace of division whatever into 
its supposed elements. It articulates with the “frontal,” parietal, 
epipterygoid, ‘‘ postorbital,” ‘‘supraorbital,”’ premaxilla and maxilla. 
Posteriorly the bone extends downward, outward and backward to the 
upper margin of the epipterygoid protuberance; externally and 
posteriorly it sends off a projection for union with the post-orbital ; 
anteriorly the bone fits into a groove on the outer side of the facial 
processes of the premaxillaries for a distance of thirty or forty milli- 
meters, and has a stout process on the outer side for union with the 
supraorbital, or whatever the element may be here. On the under 
side there is a broad, flattened, vertical plate, continuous from the 
posterior, inferior angle, and widened in the middle so as to reach the 
greater part of the way to the upper surface of the palatal bone, form- 
ing the inner wall of the orbit in large part. The plate given off for 
union with the ‘‘supraorbital” is separated by a sharp, deep notch 
from a similar process for union with the ‘‘postorbital.” The ‘‘supra- 
orbital’? bone has been crushed back over this process, so that the 
distinguishing suture can be perceived in one place only, anteriorly. 
In front of the orbit, the bone sends out a thin, triangular plate, 
which curves downward to meet the maxilla, separated from its mate 
by the premaxille. Doubtless this part represents the nasal, and per- 
haps also the lachrymal, but there are no indications of distinguishing 
sutures, and I do not believe that the nasal exists as a separate ele- 
ment in the adult plesiosaur—JI can not find that it has ever been 
described in any plesiosaur. It joins the maxille broadly and the 
‘¢supraorbital” behind; in the angle between the three bones is 
located the small external nares., Below the supraciliar plate, near 
the anterior part of the orbit, on the side of the prefrontal, there is a 
_ well-defined fossa, leading forward into the ethmoidal region, into 
which opens a small foramen from the upper surface between the pre- 
frontal and supraorbital. 
