622 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



of P. leidyi ; this is a point of generic distinction between 

 the Oligocene titanotheres. In D. 3 the planes of the 

 pre- and postzygapophyses suddenly become more 

 horizontal; this horizontal position also characterizes 

 D. 4-D. 11. In D. 14-D. 17 and in all the lumbars 

 the postzygapophyses become cylindrical or partially 

 revolute and are firmly embraced by the deeply con- 

 cave prezygapophyses as first observed by Earle. 



The relations of the vertebrae to the capitula and 

 tubercula of the ribs are clearly shown in the vertebrae 

 belonging with the skull No. 1544, and partly in those 

 belonging to the other individual, No. 1580. All the 

 ribs articulate by prominent and more or less separate 

 anterior and posterior capitular facets with the pos- 

 terior and anterior vertebral faces respectively. Ribs 



Figure 537. — Manus of Palaeosyops leidyi 



Composite fore foot from Am. Mus. 1544 and 1550 (mounted with 1544). 

 Bridger C or D. Ai, Front view; A2, phalanges of the third digit. One- 

 third natm-al size. 



1-13 exhibit projecting tubercula; in ribs 14-17 the 

 tubercula become more sessile and reduced. The con- 

 cave to flat parapophysial facets for the tubercula are 

 decidedly prominent in the anterior dorsals but become 

 less prominent and distinct or pediculate in the pos- 

 terior ones, the tubercular facet of the ribs being 

 widely separated from the capitular facets. The para- 

 pophysial processes for the articulation with the tuber- 

 cular of the ribs are very stout and downwardly ex- 

 tended, more or less triquetrous, in vertical section, 

 the anterior face being rounded and widely extended 

 outward; in the anterior dorsals the transverse meas- 

 urement across the parapophyses is 117 millimeters 

 in D. 1, 114 in D. 4, and 99 in D. S. These processes 

 gradually subside (to 60 mm. tr. in D. 17) in the 

 posterior dorsals. 



The series of ribs associated with the scapulae (Am. 

 Mus. 1580) indicate a deep and powerful chest; the 

 anterior ribs are broad and flattened externally, the 



seventh rib assumes a more rounded or trihedral 

 section, which also characterizes the eighth, ninth, and 

 tenth; the eleventh to the seventeenth are smaller, 

 with a flattened oval section; the strength of the chest 

 is attested by the presence of prominent tubercular 

 facets on the posterior ribs. The middle ribs ver- 

 tically measure 502 millimeters, not allowing for 

 curvature; the last ribs measure 260; the depth of the 

 first rib is approximately 260. 



Four sternals (No. 1580) are completely preserved 

 and a portion of the most anterior, there being five 

 preserved in all, though the exact number is not known. 

 The xiphisternum (st. 5) is very shallow, expanding 

 anteriorly and posteriorly, with a linear measurement 

 of 84 millimeters and a transverse measurement pos- 

 teriorly of 51. The three midsternals are laterally 

 compressed, with the following measurements: St. 4, 

 42 millimeters (anteroposterior) by 22 (transverse) ; 

 St. 3, 45 by 28; st. 2, 50 by 22. The presternum (st. 1) 

 is also laterally compressed; the anterior portion is 

 not preserved. The midsternebrae have the same 

 form in Oligocene titanotheres. 



The centra of C. 2-4 exhibit broadly rugose pos- 

 terior keels, which die out in C. 5. The centra of 

 C. 5-D. 2 are slightly convex inferiorly. From this 

 point backward the centra become somewhat laterally 

 compressed, especially toward the lumbars, and are not 

 keeled inferiorly; D. 5 measures 37 millimeters, D. 7, 

 39; D. 9-D. 15, about 42; D. 17, 48; L. 1, 40; L. 2, 45. 



The lumbar vertebrae are estimated in the restora- 

 tion as three in number, but there may have been 

 four lumbars and but sixteen dorsals. The trans- 

 verse processes are estimated at 174 millimeters; they 

 are of only moderate breadth. 



The sacrals are not preserved. They are present, 

 however, in a specimen referred to Palaeosyops sp. 

 (see below). 



The three anterior caudals are restored, the neural 

 arch disappears with the supposed ninth, the centra 

 of the fourth, fifth, sixth, ninth, tenth, eleventh 

 (estimated) are preserved (Am. Mus. 1544). 



Comparison with the vertebral column of Brontops 

 so far as known serves to emphasize the inference 

 based upon the study of the skull that there are few 

 resemblances except in family characters and many 

 differences, and that Palaeosyops is not in the line of 

 ancestry of this Oligocene genus. 



The structure of the scapula in this species is known 

 from that of another individual, Am. Mus. 1580, 

 associated with this mount. The general propor- 

 tions of the scapula are breadth 260 millimeters, 

 height 345, and, like the proportions of the limbs, 

 denote a slow-moving animal; the total areas of the 

 prescapular and postscapular fossae are approximately 

 equal; the prescapular fossa (origin of supraspinatus 

 muscle) is subrectangular and exhibits a marked down- 

 ward extension of the anterior border, an especial 



