250 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 92 
with a decided backward inclination. On the succeeding caudals 
these processes grow progressively shorter until on caudal 15 only 
a faint spur remains. With the disappearance of the transverse 
processes the sides of the vertebrae are flattened, resembling those of 
Iguana in that respect. Zygapophyses are short and stout, and a 
well-developed zygosphene and zygantrum are present in the anterior 
caudals, but how far they continue posteriorly cannot be determined. 
The spinous processes regularly increase in height to the neighbor- 
hood of the tenth caudal, reaching their maximum development there. 
From this point posteriorly they grow progressively shorter and be- 
come more slender. They also change in inclination in the first ten 
caudals from a type in which each strongly overhangs the succeed- 
ing vertebra to the nearly erect type of the tenth, which type then 
continues posteriorly. 
On the ventral surface close to the beginning of the ball a pair of 
short articular protuberances indicates the points of attachment for 
the chevron. 
CHEVRONS 
The chevron bones of the anterior caudal region are long, slender, 
and subequal in length with the spinous processes. They articulate 
intervertebrately, but more especially with the anterior vertebra of 
each pair. The first chevron appears to be articulated with the third 
and fourth caudal instead of the second and third, as in 7guana. 
RIBS 
All the presacral vertebrae with the exception of the atlas, and pos- 
sibly the axis, appear to have been rib bearing. The fifth cervical 
vertebra of the type specimen has the rib of the left side preserved 
in articulated position. It is short, having a head widely expanded 
dorsoventrally, with a cupped articular end that fully covers the 
elongated costal facet of the vertebra. The downwardly curved 
shaft tapers rapidly to a pointed distal end. Beginning well toward 
the proximal end on the median anterior surface an overhanging 
ridge projects prominently forward from this side. This ridge has 
a diagonal downward trend and merges into the outer ventral mar- 
gin of the bone. Two cervical ribs belong to specimen U.S.N.M. No. 
15568, one of which, as indicated by its smaller size, pertains to a 
cervical in advance of the fifth. It has a greatest length of 15 mm. 
On the left side of specimen U.S.N.M. No. 15816 cervical ribs 4 and 
5 are preserved nearly in articulated position. 
The thoracic ribs are best preserved in specimen U.S.N.M. No. 
15816, as shown in plate 25. In all, 48 ribs are present, of which 30 
are complete or nearly so, and practically all have been preserved 
articulated with their respective vertebrae. In specimen U.S.N.M. 
No. 15568 18 ribs are preserved; 9 of these on the left side are articu- 
