WILLISTON: RESTORATION OF ORNITHOSTOMA (PTERANODON). 39 
Skull. 
The shape and structure of the skull I have described in previous 
Papers. In the present species the total length of this part of the 
Skeleton was considerably less than four feet. A most careful ex- 
amination of the alveolar borders of both maxilla and mandibles, 
has revealed no indications of teeth, even rudimentary ones. The 
Position of the occipital condyle is such that the head might have 
been flexed to an acute angle upon the neck. In the figure here 
Siven the width of the head is less than has been heretofore figured, 
but it is certainly more nearly correct. 
Vertebras. 
The number of cervical vertebra is seven, and, in all probability, 
not more. The atlas and axis I have never seen. It is probable 
that they do not differ materially from the bones of Myctodactylus, 
as already described by me in a previous paper. The third cervical 
Is the longest, the others successively decreasing in length. The 
first and second dorsal are short, and bear well developed, double- 
headed ribs. The difference between the last cervical and first 
dorsal is considerable. The third, fourth and fifth dorsals, if my 
determination is correct, have the centra and ribs co-ossified for 
the support of the scapula. The succeeding vertebre are short, 
Cylindrical bones, with a hemispherical ball, and with elongated 
transverse processes situated high upon the arch. The number is 
indefinite. 
Fourth cervical vertebra. 
The centrum is elongated. The ball is much broader than high, 
and strongly convex in both directions; its upper border is convex, 
but the inferior margin is emarginate on each side. On each side 
there is a stout process, jutting downwards and backwards from the 
Side of the centrum on each side, having on the posterior surface 
4 concave articular facet, oval in shape and touching or slightly 
Separated from the articular surface of the ball. The facet looks 
downwards, backwards, and outwards. The under side of the cen- 
trum, between the two processes, is concave. The corresponding 
articular facets on the anterior end of the centrum are somewhat 
Smaller, are convex and distinctly separated from the concavity of 
the centrum. The articulation of the centra with each other thus 
depends upon three distinct, or nearly distinct surfaces, the lateral 
inferior ones convex on the cup end, concave on the ball end. 
Such a mode of articulation would seem to limit the motion to one 
in 
a vertical, antero-posterior plane, while greatly strengthening 
