Apr. 1903. North American Plesiosaurs — Willistok. 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 I 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 maxillae in the 

 way they are figured by Sollas in Plesiosaurus.* 



The posterior pointed extremities of the vomits 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 maxilla 1 . Unfor- 

 tunately this part of the skull has been injured somewhat before 

 removal, and the complete structure here cannot be determined. 



The so-called " parasphetwid" 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. Anteri- 

 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. Geo!. Soc. 1881. p. 475, '• 12- 



