420 O. C. Marsh—American Jurassic Dinosaurs. 
union of the spines of several vertebrae. In front, it shows 
rugosities for the ligament uniting it to the adjoining vertebra, 
and its posterior margin likewise indicates a similar union with 
the first caudal. In this genus, as in all the Sawropoda, each 
vertebra of the sacrum supports its own transverse processes. 
As shown in Plate X VI, the articulation for the ilium is forme 
by the codssification of the distal ends of the transverse 
processes. 1e neural canal is much enlarged in the sacrum, 
but proportionally less than in Stegosaurus. 
THe CaupAL VERTEBRA. 
In the present species, the three vertebrae next behind the 
sacrum have moderate sized cavities between the base of the 
neural arch and the transverse processes. These shallow pock- 
ets extend into the base of the processes, but the centra proper 
are solid. All the other caudals have the centra, processes, and 
spines composed of dense bone. The fourth caudal vertebra, 
represented in Plate XVII, figures 1 and 2, is solid through- 
out, and the same is true of the chevron, figures 3 and 4. The 
neural spines of the anterior caudal vertebra are elevated and 
massive. The summit is cruciform in outline, due to the four 
strong butresses which unite to form it. 
The median caudals all have low weak spines, and no 
transverse processes. The posterior caudals are elongate, and 
without spines or zygapophyses, 
Tue Petvic ARcH. 
lage. The ischium is more slender than the pubis, and has its 
lower end expanded for symphysial union with the one on the 
other side. This pelvis is more like that of Atlantosaurus 
than any other of the known genera of the Sawropoda. The 
three bones shown in Plate XVIII were found nearly in the 
position represented, 
