94 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



The pelvis is represented by only a single specimen, derived from an 

 immature animal and lacking the anterior portion of the iliac plate. The 

 ilium, so far as it is preserved, resembles that of Proterotherumi, but has 

 an even shorter peduncle, from which the anterior expansion broadens out 

 more abruptly ; the ischial border is sharp and well defined, but the pubic 

 border is very short and the acetabular border is obscure : the gluteal 

 surface is but slightly concave and there is no ilio-pectineal spine, but there 

 is a roughened tubercle at the anterior margin of the acetabulum, presu- 

 mably for the attachment of the gluteus minimus muscle. The ischium is 

 short, slender and laterally compressed, expanding posteriorly into a broad, 

 thin and strongly everted plate, which bears a small tuberosity : the sciatic 

 notch is very feebly indicated. The pubis is short, compressed and plate- 

 like, but has a slender backward prolongation on the ventral side, which 

 makes the symphysis long. The obturator foramen is a long, narrow 

 oval, smaller than in Proterotheriuni. 



The femur (PI. XII, figs. 12, 120) is remarkably equine in appearance, 

 strongly resembling that of Mesohippus. The head is small and placed 

 upon a short, distinct neck, and is thus less sessile than in Proterotherimn, 

 more antroverted and with the pit for the round ligament less extended 

 proximally, but of similar ovoid shape, with the long axis directed antero- 

 posteriorly ; while the bridge between the head and the great trochanter 

 is more deeply notched. The great trochanter is much more prominent 

 and rises much higher above the head than in the last named genus and 

 the digital fossa, though hardly so deep, is more elongate ; "the second 

 trochanter is a long, thin ridge, gradually dying away upon the shaft ; its 

 proximal portion is not so thickened and rugose as m Proterotheriuni ; the 

 third trochanter is rather less prominent and antroverted, but longer proxi- 

 mo-distally than in the latter. The shaft is moderately stout and has a 

 slight sigmoid curvature ; the linea aspera externa is less developed than in 

 Proterotheriuni , but the fossa for the plantaris muscle is even deeper and 

 more distinct. The rotular groove is narrower and slightly asymmetrical, 

 owing to the somewhat greater elevation of the internal border, and there 

 is a deep suprapatellar fossa. The condyles are widely separated and 

 asymmetrical, the external one being larger and more convex ; the articu- 

 lar surface is not continuous between the condyles and the rotular groove, 

 but is interrupted by a narrow, non-articular space on each side. 



The patella is rather short proximo-distally and relatively broad and 



