Sinclair: typotheria of the santa cruz beds. 
53 
deep concavities on either side of the keel are bounded externally by the 
inferior edges of the transverse processes. 
The slender spines of the remaining cervicals increase in length pos- 
teriorly. Anteriorly, they are directed vertically, but posteriorly they 
incline backward like the anterior dorsal spines. They are seldom com- 
pletely preserved. Hatchet-shaped transverse processes begin on the 
third cervical and the differentiation into diapophysis and inferior lamina 
is already apparent in the fourth. The diapophysis alone is present in 
the seventh. Interiorly, the centra of the anterior members of the series 
are strongly keeled, but the keel soon bifurcates, terminating posteriorly 
in a pair of tubercles. These tubercles are absent in the fifth, sixth and 
seventh cervicals and the centra are broadly keeled. 
The dorso-lumbar vertebral formula is definitely known to be twenty- 
two, of which fifteen are dorsals. The anterior dorsals have long, slender, 
posteriorly directed spines, which, at about the sixth dorsal, begin to 
decrease in length, to increase in antero-posterior diameter and to expand 
at the tip into a dorsally flattened, triangular area. From the ninth dor- 
sal onward, the spines are very broad antero-posteriorly, with the tips flat- 
tened and oblong in outline. The backward inclination of the neural 
spines changes between the tenth and eleventh dorsals. The lumbar 
spines are similar to those of the posterior dorsals, but in a single speci- 
men referred to /. extension (No. 15,041) the tips of the spines are broadly 
expanded dorsally, irregular in outline and strongly rugose. In another 
specimen (No. 9557 American Museum collection) which it has not been 
possible to determine specifically, the neural spines of the lumbars are 
bifid posteriorly and the dorsal flattened area is quite narrow. The 
transverse processes are broad, flat blades, curving forward. Prominent 
metapophyses and anapophyses are present on the posterior dorsals and 
lumbars, the anapophyses decreasing in length in the posterior members 
of the lumbar series. Strongly interlocking zygapophyses are a feature 
of the lumbar and posterior dorsal vertebrae. 
Five vertebrae form the sacrum, three of which are in contact with the 
ilium and two belong to the caudal series (PI. VI, fig. 11). The second 
and third sacrals and the caudals are firmly coossified by their neural 
arches, zygapophyses, transverse processes and centra, while the first 
sacral is free. The coossified neural spines of the sacral complex form 
an elongated plate, flattened dorsally. 
