EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



655 



nent than in Menodus; pronator ridge rugose but not 

 projecting; supratrochlear fossa deeply excavated, 

 and trochlear process somewhat oblique to main axis 

 of shaft. 



The ulna and radius are complete in the same 

 specimen (Princeton Mus. 10396, fig. 594) and taken 

 together indicate a rather long and slender forearm. 

 Other characters are as follows: Relative diameters 



' (nv.J {cb) 

 -Astragalus and oalcaneum of Dipla 

 codon or Prolitanolheriuvi 



Princeton Mus. 10396; Uinta C. Left astragalus and calcaneum, 

 crushed (?). Ai, Front view; As, outer side view. One-third 

 natural size. 



of distal facets of radius and ulna about as 5 to 2, 

 ulna with a very stout, rugose olecranon, with the 

 posterior border presenting a single concave curvature, 

 with shaft triangular in midsection, and a deep groove 

 on the anterior face. The radius in midsection of the 

 shaft is suboval anteriorly and flattened posteriorly. 

 Facet for the entocondyle of the humerus with a deep 

 anteroposterior diameter. The manus (Princeton 

 Mus. 10396, fig. 594) lacks the carpus. The meta- 

 carpus exhibits a high, stilted tetradactyl or digiti- 

 grade type, the distinctive feature of the foot consist- 

 ing in the subequal size of the second and fifth 

 metacarpals, which brings the working median axis 

 of the manus between the third and fourth digits 

 instead of through the middle or third digit. This 

 is a decided progression upon any known Bridger type. 

 The measurements are as follows: Mtc III, length 

 180 millimeters; Mtc V, 130. Other measurements 

 may be taken from the figure. 



The femur belongs to another animal (Princeton 

 Mus. 10395). The original drawing represents bones 

 belonging to two individuals of the same size drawn 

 in combination. This bone presents the essential 

 characters of the femora of titanotheres. 



The tibia of the same animal (Princeton Mus. 

 10395) is about five-sevenths the length of the femur; 

 the cnemial crest is moderately prominent; there is 

 the usual triangular section of the shaft just below 

 the crest passing into an oval section in the lower 

 third; the proximal and distal faces are too much 

 worn to admit of description. 

 101959— 29— VOL 1 45 



The somewhat crushed astragalus and calcaneum o 

 a tarsus in the Princeton Museum (fig. 595) are of 

 great interest. The principal feature of the calcaneum 

 is the extremely narrow, deep, and elongate tuber 

 calcis, which has an unusually flattened section. There 

 is also a distinct fibular facet, and the calcaneum forms 

 part of the tibial trochlea. The astragalus rests upon 

 over one- third of the upper surface of the cuboid; 

 the three astragalar facets — the ectal, sustentacular, 

 and inferior — are entirely distinct. 



An ilium (Am. Mus. 2084) may also be referred 

 to this species. The measurements (estimated) are as 

 follows: Transverse width across ossa innominata 665 

 millimeters, total width of superior border of ilium 

 340, length of anterior border to acetabulum 335. 

 The superior border is well rounded. 



A tibia (Am. Mus. 2056), rather short and massive, 

 having a total length of 325 millimeters, is provision- 

 ally referred to the same species, P. emarginatum. 



SUBFAMILY BEONTOPIFAE? 



Bones provisionally referred to Protitanotherlum superbum 



A radius (Am. Mus. 2035) exhibits a length of 425 

 millimeters and perhaps may be referred to P. super- 

 lum. The length of the radius in the Princeton 

 Museum provisionally referred to JDiplacodon elatus 

 is 350 millimeters. 



A large astragalus (Am-. Mus. 2030) has the breadth 

 (width across trochlear keels, 700 mm.) that seems 

 appropriate for this species. The cuboid facet is very 

 progressive (fig. 596). 



Figure 596.— Left astragalus of ProlUanoOierium 

 superbum 



Am. Mus. 2030; Uinta C. Front and rear views. One-third 

 natural size. 



SUBFAMILY DIPLACODONTINAE 



Pelvis referred to Diplacodon elatus 



The only portions of the skeleton certainly associated 

 with the type of D. elatus are the cervical vertebrae 

 associated with the type skull in the Yale Museum 

 (No. 10320). 



The pelvis (Princeton Mus. 10393, fig. 597) origi- 

 nally referred to Diplacodon elatus by Scott and Osborn 

 in "The Mammalia of the Uinta formation" (1890.7, 

 pp. 516, 517) may still be referred provisionally to 

 that species. The marked characteristic of this 

 pelvis is the great length of the ossa innominata as 

 compared with their breadth. The ilia did not expand 



