62 FiELD COoLUMBIAN. MusEUM—GEOoOLOGY, VoL. II. 
4 
The increase in length of the cervical vertebre is slight, as will be 
seen from the table of measurements. The articular margin of the 
vertebrae, throughout both the cervical and dorsal series, is sharp, 
not rounded for a continuation of the cartilaginous surface, as is so 
often the case among plesiosaurs. The ends, as seen in the third 
vertebra, are distinctly though not deeply concave. The ventral 
vascular foramina, so characteristic of plesiosaur vertebra, appear to 
be wanting throughout the whole series, nor is there the slightest 
indication of a median ridge and lateral grooves. The lower margin 
of the rib articulation approaches the ventral plane in the early 
cervicals; but ascends somewhat on the sides of the vertebra in the 
last cervical. se ipa. 
Twenty-two dorsal vertebre are preserved in natural sequence. 
Because of the decrease in the length of the transverse process in the 
late dorsals, it does not seem probable that more than eight or ten 
presacral vertebre could be missing, making altogether about thirty, 
the usual number of dorsal vertebrae. The length of the centra 
increases more rapidly, though gradually, in the early dorsals, and 
then remains constant throughout the remainder of the series. The 
centra are deeply concave below and on the sides, expanding out- 
wardly on the sides above to meet the sutural surface for the arch. 
The surface of the centra is nearly smooth, with but slight indications 
of crenulations before the articular margins. 
Riss.—The ribs throughout are single-headed, and of the usual 
plesiosaurian type, though proportionally short in the thoracic region. 
The axial rib is flattened spatulate at the distal extremity; massive at 
the proximal. The lower surface is nearly flat, the upper surface 
deeply concave, the anterior border gently, the posterior border deeply 
concave. The rib of the third vertebra is more expanded distally, 
with the distal posterior margin somewhat more produced, and the 
distal border thinned. The fourth rib is more expanded distally, with 
a more pronounced distal expansion, and the distal border seems to 
be thickened for cartilage. The next four or five ribs differ only 
slightly from the preceding ones. The rib of the tenth vertebre is 
more elongated and slender. The attachment to the centrum is 
sessile or nearly so, the head inserted in a shallow pit. In the 
eleventh vertebra there is a distinct exogenous process, standing out 
twenty or twenty-five millimeters from the surface of the centrum to 
the end of which is attached the rib. This process is equally as 
prominent, or more prominent on the next two centra, the twelfth 
and thirteenth. The rib of the twelfth vertebra is intermediate in 
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