634 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



into an angulate process, and in inferior view the 

 bone is more oval, whereas in Palaeosyops it is more 

 or less rhomboid. In most of these characters the 

 trapezoid is, on the whole, nearer to that of Mesati- 

 rJiinus than to that of Palaeosyops. The trapezium 

 is not known, but to judge from the character of the 

 trapezium facets on the trapezoid it probably ap- 

 proached nearer to the pear-shaped trapezium of 

 Mesatirhinus than to the broad ovoid trapezium of 

 Palaeosyops. The magnum (Am. Mus. 1587, 12204) 

 has a relatively narrower front face than ia Palaeosyops, 

 and its scaphoid facet is more vertical than horizontal; 

 the facet for Mtc II is larger, the facet for Mtc III 

 in inferior view is more straight-sided, broader pos- 

 teriorly, and less broad anteriorly; the posterior 

 hook of the magnum is broadly spatulate instead of 

 posteriorly pointed; the capitellum, or posterosupe- 

 rior head for the scaphoid and lunar, in Am. Mus. 



relatively wider posteriorly, except in Mtc V; Mtc II 

 is a little shorter than in Palaeosyops, but Mtc IV and 

 V are as long or longer. The dimensions of the 

 metacarpals compared with those of the supposed 

 Palaeosyops copei?. Am. Mus. 12205, are as follows: 



Measurements of metacarpals in Manteoceras manteoceras and 

 Palaeosyops copei?, in millimeters 



Figure 555. — Pelvis of Manteoceras? 



.'.ntero-inferior aspect of pelvis. Am. Mus. 235!!; Washakie Basin, level B 1. One- 

 sLxth natural size. 



12204 appears more globose than in Palaeosyops, but 

 this character is not so well shown ia Am. Mus. 1587. 

 The unciform (Am. Mus. 1587, 12216) is proportion- 

 ately narrower than in Palaeosyops but broader and 

 deeper vertically than in Mesatirhinus; in top view 

 the lunar facet is subquadrate, whereas in Palaeosyops 

 it is more rhomboid, being produced postero-externaUy 

 and antero-internally; the cuneiform facet is not so 

 wide supero-externally, being thus of more even diam- 

 eter than in Palaeosyops, in which it is wide supero- 

 internally and narrow supero-externally. The tuber, 

 or posterior process of the unciform, on its internal 

 face meets the main body of the bone at right angles, 

 whereas in Palaeosyops it slopes gently down and 

 meets the posterior face on an open angle. 



The metacarpals (Am. Mus. 12216, 1587, 12204 in 

 part) are relatively longer, narrower, and more 

 straight-sided than in Palaeosyops; their distal (pha- 

 langeal) facets are transversely subcylindrical rather 

 than subglobose; their proximal or carpal facets are 



M. manteoceras 



II, length 



II, pro.ximal ■nidth (front) 



II, distal width (maximum) _ _ 



III, length ' 



III, proximal width (front) __ 



III, distal width 



IV, length ! 



IV, proximal width (front) 



IV, distal width (maximum) _ 



V, length I 



V, proximal width (front) 



V, distal width (maximum) _ _ 



104 

 27 



27 



P. copei, 



Am. Mus 



12205 



96 

 35 



42 

 107 



38 

 93 

 31 

 40 

 75 

 24 

 35 



The phalanges are much smaller, relatively shorter, 

 broader distally, and deeper vertically than in Palaeo- 

 syops: 



Comparative measurements of proximal phalanx of digit HI in 

 Manteoceras manteoceras and Palaeosyops copei?, in millimeters 



Length 



Transverse proximal 



Vertical proximal 



Transverse distal 



M. manteo- P. copei, 

 ceras, 1 Am. Mus. 

 .\m. Mus. 1587 12205 



36 

 35 

 24 

 27 



The distal phalanges are short and widely expanded, 

 truncate, and deeply cleft distally, in contrast to the 

 longer, distally rounded to subpointed, rather feebly 

 cleft unguals of Palaeosyops. These differences, 

 considered in connection with the narrower, straight- 

 toed manus, ia contrast to the broad spreading-toed 

 manus of Palaeosyops, poiat to tapir-hke rather than 

 hippopotamus-lilve habits and tend also to confirm 

 not only the hypothesis that Palaeosyops was semi- 

 aquatic but also the hypothesis that Manteoceras was 

 allied to Mesatirhinus and to the Oligocene titano- 

 theres. 



A well-preserved pelvis (Anr. Mus. 2358) froai the 

 Washakie Basin is provisioaaUy referred to Man- 

 teoceras. The measurements are as follows: Pelvis 

 transverse 530 millimeters, anteroposterior 450 ; pubo- 

 ischiadic symphysis 170. Only three sacral vertebrae 

 are preserved out of the probable four. This speci- 

 men illustrates the deeply revolute character of the 

 prezygapophyses of the first sacral vertebra, the trans- 



