SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 27 



Despite its resemblance to that of the horses, the manus of Diadiaphonts 

 is fundamentally different. In the carpus we find a retention of semi-taxeo- 

 pod conditions, in that the lunar is far removed from the unciform and 

 rests entirely upon the magnum. The carpals of the distal row, especially 

 the magnum, are much narrower than in the equine manus, while the 

 large, functional third metacarpal supports only the magnum, not extend- 

 ing, even on the palmar side, beneath the unciform on one side and the 

 trapezoid on the other, as it so conspicuously does in the horses, and the 

 second metacarpal retains its full connection with the magnum. As com- 

 pared with that of the horses, the metacarpal of the median digit is rela- 

 tively short, while the phalanges of this digit are very elongate. In brief, 

 the Santa Cruz genus, despite its markedly advanced degree of special- 

 ization in foot-structure, yet retains a surprising number of primitive 

 characteristics. 



Like so many other elements of the appendicular skeleton, the pelvis 

 (PI. I) has a decidedly equine appearance. The ilium has a shorter and 

 much broader peduncle, which expands anteriorly into a broad plate of very 

 similar shape to that of the horses, with median portion sharply curved up- 

 ward, to articulate with the sacrum, much as in the horse, but the external por- 

 tion has no such heavy crista as in the latter : the iliac surface is very broad 

 and the ilio-pectineal process is prominent and projects almost directly 

 inward. The acetabulum has a prominent border, which anteriorly be- 

 comes very heavy and rugose ; it is extensively invaded from the ventral side 

 by a large and deep sulcus for the round ligament. The ischium is rather 

 short and slender and its dorsal ramus is trihedral, flattening posteriorly 

 into a strongly everted plate ; the tuberosity is a conspicuous, but rather 

 slender spine-like process. The pubis is short, stout and much depressed, 

 and forms a long symphysis with its fellow of the opposite side. The 

 obturator foramen is relatively quite small and of irregularly oval shape. 



Of all the bones in the skeleton, the one which is most strikingly horse- 

 like in character is the femur (PI. Ill, fig. 6). The head is quite small, 

 and of depressed and somewhat irregular shape, and sessile ; the pit for 

 the round ligament is a V-shaped incision on the postero-internal side of 

 the head, much like that of the horse in shape and position, but smaller 

 and shallower. The great trochanter is very large, rising high above the 

 head, but less massive than in Eqtnis, and not divided by a sulcus into 

 two parts, as it is in the horses ; the digital fossa is large and deep : the 



