Apr. 1903. NortTH AMERICAN PLESIOSAURS—WILLISTON. 61 
is usually called the presphenoid. Such perfect and persistent 
ossification of the parasphenoid, scarcely found elsewhere among the 
reptilia, unless it be the snakes, is in any case remarkable. Why 
should it be persistent in separating such persistent foramina, unless 
the openings were of functional importance? One would expect 
that the pterygoids would have united along the whole median 
line, as in the Nothosauria, or that they should have closed up 
in front of the basisphenoid, as in the Chelonia.  Sollas objects 
to this posterior position of the nostrils, because there is no ossified 
canal for the air passages, as in the crocodiles; but his specimen, as 
ours, would call for a canal running in the opposite direction, from 
the posteriorly situated external nares anteriorly to the internal open- 
ings, and, in the present species, this canal would have been eight or 
more inches in length. And why may not the canal have been 
cartilaginous in either case? 
MANpiBte.— The mandibles are nearly in place on the under side 
of the skull. They are a little compressed from above downward. 
The symphysis is short, the two jaws meeting in a considerable angle. 
The portion in front of the posterior end of the symphysis has been 
somewhat injured in the specimen, so that the precise shape and 
length can not be ascertained. The angular extends posteriorly into 
a relatively short process; the expansion below the cotylar cavity 
is rounded. In front of the cavity, the angular extends forward to 
within six inches of the symphysial angle, terminating in a slender, 
sharp end. From a little in front of the middle of the ramus it is 
excluded from the inner surface. In front of the cotylar cavity the 
greater width of the outer surface is composed of the surangular. 
Between these two bones, the dentary sends a long, slender process 
backward to within six inches of the cotylar cavity. 
Length of skull to end of aaa : poi DA Re iy 
Length of skull to condyle : : mn: 
Width of skull between outer margins of auateats .28 m. 
VeRTEBR£.—The atlanto-axial complex is thoroughly united, with- 
out indications of*sutural division. The axial rib appears to be 
united with the axis only, though it may come in contact with the 
axial intercentrum. The atlas is convex from side to side, without 
indication of a median carina. The other cervical centra, as seen 
from below, are nearly flat, with a slight convexity in the middle, and 
a slight concavity on either side before the sutural surface for the rib. 
This flatness is a natural character and not due to compression. The 
median convexity increases gradually throughout the cervical series. 
