Sinclair: typotheria of the santa cruz beds. 
75 
The mandibular rami (PI. I, figs, i, 5) are firmly coossified at the sym- 
physis, producing a long, spout-like depression, the slope of which is con- 
tinued forward by the pronate incisors. The horizontal ramus is some- 
what thicker than in Protypotherium and increases more gradually in 
depth posteriorly. The masseteric fossa extends to the angular margin, 
limited anteriorly and inferiorly by a strong everted flange, with hook- 
shaped anterior extremity. The angular portion of the mandible is deep, 
projecting posteriorly beyond the condyle and inferiorly below the lower 
border of the horizontal ramus, with sharply convexAutline. The coronoid 
process is imperfectly preserved in all the specimens examined. It is 
thin and narrow, projecting well above the condyle, from which it is sepa- 
rated by a narrow sigmoid notch. Anteriorly, the coronoid border is 
slightly convex, rising almost vertically from the alveolar margin, in strik- 
ing contrast with its strong forward inclination in Protypotherium. The 
condylar surface is a flattened oval in outline, wider externally than 
internally, convex in all dimensions and presenting forward. The pos- 
terior portion of the capitulum is not occupied by an articular surface, but 
by a roughened area of irregular outline fitting into the postglenoid fossa, 
as in Protypotherium. The neck is far less sharply differentiated than in 
the last named genus. Externally, on either side, there is always a large 
mental foramen (sometimes double) in the symphysial region, and several 
small foramina varying in number and position on the external surface of 
the horizontal ramus. Internally, the opening of the inferior dental canal 
is large and is rendered doubly conspicuous by a long, deep groove, lead- 
ing into it from above. 
Vertebral column (PI. II, figs. 22-27). — The vertebral column is very 
incompletely known. The atlas (PI. II, figs. 25-27) differs from that of 
. Protypotherium in the shape of the transverse processes and the arrange- 
ment of the vertebral foramina. The transverse processes are fan-shaped 
expansions, with lobate free border, and are rather sharply constricted at 
the base. The posterior third of the base of the process is thickened, the 
arterial canal entering at the margin of the posterior constriction and 
emerging on the lower surface of the process. Anterior to the point of 
emergence of the canal, the thickness of the basal portion of the process 
greatly decreases. In the atlas of Protypotherium this canal is not 
present. The neuro-arterial canal sometimes lacks the anterior bony 
bridge, appearing as a deep groove. Both conditions occur in the same 
