Apr. 1903... NortrH AMERICAN. PLESIOSAURS—WILLISTON. 15 
quence, the fragility of the skull was such that it was not deemed 
prudent to mount it with the remainder of the skeleton. A model of 
it was therefore made, based upon my drawings and studies, and 
which, I think, represents the skull very nearly as it must have been 
during life. Its width in all parts may not have been accurately 
determined, but the discrepancies from the reality can not be great. 
The premaxillaries are separated from each other distinctly by 
suture, the long facial processes apparently lying in contact with each 
other without close union. The suture separating them from the 
maxilla begins just back of the sixth tooth; it curves upward and 
backward for a short distance, and then runs parallel with the upper 
border as far back as the narial opening, whence the margin runs more 
obliquely to the tip of the processes above the middle of the orbit. 
Each premaxilla bears six teeth, which are among the largest of the 
jaws, and are all of nearly uniform size, the first one curved forward. 
The facial process is slender, flattened on its opposing, sutural sur- 
face, and with its external, convex surface distinctly striated longi- 
-tudinally. The dentigerous portion is convex, pitted toward the 
anterior patt, and about twenty- five millimeters in height, opposite 
the last tooth. The relations of the bone on the palatal surface can 
not be determined. 
The maxz//e are long and narrow on the facial surface, and 
very narrow on the palatal surface, at least posteriorly. They bear 
twenty teeth on each side, the first ten or eleven of which are 
of nearly equal size, and scarcely smaller than those of the pre- 
maxilla. The posterior ten teeth are crowded, occupying a 
space less than one-half that of the preceding ten, and they are 
smaller. The greatest width of the maxilla on the facial surface 
—about twenty-five millimeters—is at about seventy millimeters in 
front of the orbit, whence the bone narrows to a width of ten milli- 
meters below the anterior border of the orbit. Below the orbit, the 
bone extends asa narrow bar, becoming slightly narrower posteriorly, 
before the beginning of the jugal suture. Beyond this, it flattens 
posteriorly to near its extremity, which is about midway of the tem- 
poral bar, and one hundred millimeters beyond the last tooth. 
There are twenty-five or twenty-six teeth in each jaw. They are 
inserted by a long fang, the pulp cavity of which occupies more than 
one-third of the diameter, extending a short distance into the crown. 
In the largest teeth, the crown is about twenty millimeters in length, . 
with a diameter at the base of six millimeters. The crown is rela- 
tively slender, strongly convex anteriorly, sharply conical, and with 
slender, delicate, longitudinal striae, except on the outer, anterior 
