Apr. 1903. NortTH AMERICAN PLESIOSAURS—WILLISTON. 59 
goid on the inner side and behind, the posterior suture descending on 
the side of the projecting process of the pterygoid. To what extent 
the bone enters into the abutting surface for the mandible I could not 
determine. Anteriorly the bone joins the palatine by a clearly 
marked suture. Its outer border posteriorly is rounded and seems to 
be free, forming a part of the border of the posterior palatine vacuity, 
but this can not be determined without further excavation of the 
matrix. The outer attachment of the bone (doubtless to-the jugal 
and maxilla) cannot be determined. 
The palatines are long flat bones which meet for a considerable 
distance in a median suture in front of the pterygoids, a feature hith- 
erto unknown among the plesiosaurs. In front this median suture 
divaricates to admit the pointed extremities of the vomers. A little 
distance from the interpalatine suture, near its middle, there are, on 
either side, two or three small, round foramina. The outer border 
of the palatines continues the border of the ectopterygoids throughout 
and is continuous, apparently with the lateral border of the vomers. 
How far this apparent border in the specimen represents the real 
border of the bone cannot be determined without additional excava- 
tion of the matrix, here filling in a narrow space between the apparent 
margin and the mandible. It is possible that there may be no free 
border, though | think it probable that there is a smaller or larger 
posterior palatine vacuity on each side posteriorly. It is probable 
that the sides of the bones turn upwards to meet the maxille in the 
way they are figured by Sollas in Pleszosaurus.* 
The posterior pointed extremities of the zvomers are seen in the 
middle in front, enclosed between the V-shaped suture of the pala- 
tines. The suture seems to be visible to the border of the palatine 
and includes no part of a narial opening. The nares hence must be 
situated far forward between the vomers and the maxille. Unfor- 
tunately this part of the skull has been injured somewhat before 
removal, and the complete structure here cannot be determined. 
The so-called ‘‘ parasphenoid”’ is different from that element in 
other plesiosaurs. It is a single bone separating the interpterygoid 
vacuities. As seen from below, it ‘is spindle-shaped, narrow in the 
middle, moderately expanded at either extremity. Posteriorly it is. 
joined by a clearly marked suture with the basisphenoid. Antert- 
orly it joins the two pterygoids in the entrant angles, but does not 
extend much, if any, beyond the angle. The vacuities separated by 
this bone are long and oval, situated at the bottom of the fossa 
already described, between the pterygoids and in front of the basi-. 
*Quart. Journ. Geol. Soc. 1881, p. 475, f. 12. 
