Sinclair: typotheria of the santa cruz beds. 
9i 
thirteenth dorsal, and has a broad, vertically directed spine. It is followed 
by two dorsals, in which the spines are similar in shape to those of the 
anterior lumbars and are directed forward. The spines of the posterior 
lumbars are very heavy, strongly inclined forward and deeply grooved 
posteriorly, with a prominent tubercle developed on either side of the 
groove about half way between the posterior zygapophyses and the tip of 
the spine (PI. X, fig. 31). The transverse processes are broad, flat blades, 
with truncated extremities, curving outward and forward. Prominent 
anapophyses are developed on the posterior dorsals and anterior lumbars, 
decreasing in size posteriorly. The zygapophyses in the posterior dorsals 
and in the lumbar series interlock as strongly as in Hegetotherium. 
Five vertebrae are coossified in the sacrum, of which three are in con- 
tact with the ilium and two are referable to the caudal series. In all the 
specimens (Nos. 9242, 9283, 9481 of the American Museum collection) 
the neural spines of the anterior sacrals have been broken off. Those of 
the posterior sacral and the coossified caudals are very heavy, with flat 
summits (PI. X, fig. 18). Little can be said regarding the tail, as but 
four free caudals close to the sacrum are preserved in No. 9242. These 
are elongated, with little indication of transverse processes, and suggest a 
short tail. 
Appendicular Skeleton. — The scapula is so imperfectly preserved in all 
the specimens available that its shape cannot be determined. In the 
restored skeleton of Pachyrukhos (PI. XI) it has been given approximately 
the same shape as in Protypothevimn. The spine is high and the meta- 
cromion robust. The clavicle is a slender rib-like element compressed 
laterally and gently arched longitudinally (PI. X, fig. 5). At the distal 
end it expands, but has been so damaged by fracture that its exact shape 
cannot be ascertained. 
The humerus (PI. X, fig. 1 1 ) is almost a miniature of that of Hegeto- 
therium. The head is large, overhanging the shaft posteriorly. The 
greater tuberosity is prominent, rising above the level of the head, as in 
Hegetotherium , while the lesser tuberosity is inconspicuous. Distally, the 
correspondence with Hegetotherium is very close. There is the same well- 
defined separation of the articular surface into trochlea and capitellum, 
the same elongation of the inner lip of the trochlea, strong development 
of the inner epicondyle and short, but sharply defined, supinator ridge. 
An internal epicondylar foramen is present and in all the specimens 
