EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



675 



rugose and expand distally, especially on D. 2-4, 

 somewhat as in the rhinoceros. The terminal phalanx 

 of D. 3 measures 55 millimeters transversely. 



As the pelvis and hind limb of this mounted skele- 

 ton are not associated with the leading specimen and 

 not certainly determinable as to genus and species a 

 detailed description of these parts may be omitted. 

 These specimens bear the following American Mu- 

 seum numbers: Pelvis, 1065; left femur, 1443; right 

 femur, 1442; left tibia, 1075; right tibia and fibula, 

 493; left fibula, 1071; pes, 1073 and 1076. 



Mounted skeleton of Brontops brachycephalus? in the Victoria 

 Memorial Museum, Ottawa 



The author has had no opportunity of studying 

 this specimen, but a figure of it has been supplied 

 through the courtesy of Mr. Harlan I. Smith and Mr. 

 Charles M. Sternberg, of the Victoria Memorial 

 Museum. (See figs. 610, 611.) 



Manus provisionally referred to Brontops robustus? 



A large manus in the American Museum (No. 

 1046''^) is provisionally referred to this genus and 

 species. As compared with the manus of the mounted 

 skeleton already described (Am. Mus. 518) its meas- 

 urements are as follows: 



Comparative measurements of manus referred to Brontops 

 robustus, in millimeters 



Diploclonus Marsh 



Skeleton of Diploclonus tyleri Lull 



In the Amherst College Museum is an important 

 though incomplete skeleton (No. 327), the type of 

 Diploclonus tyleri Lull, which was found in Spring 

 Draw Basin, about 10 miles from the mouth of Bear 

 Creek, a tributary of Cheyenne River, S. Dak. The 



« Parts of two individuals were included under the number 10!6, there being one 

 right and two left manus. 



specimen was found lying 35 feet above the base of 

 some 200 feet of Titanotherium-he&img beds. The 

 skull and dentition are described on page 503. 



The material includes a skull and lower jaw, the 

 atlas and axis, two cervical vertebrae, nine dorsals, 

 thirteen ribs, and the greater part of the fore and 

 hind limbs. Lull's description (Lull, 1905.1, pp. 448- 

 456) of the vertebrae and limb bones is as follows: 



The atlas. — The atlas is a broad, heavy bone, with wide 

 articular facets and expanded transverse processes. The spine 

 is extremely low, and the short truncated hypapophysis extends 

 bacliward. Of the foramina, only that for the dorsal root of 

 the first cervical nerve is present, the ventral one, well shown 

 in Palaeosyops," being here represented by a deep notch as in 

 the rhinoceros, which our specimen also resembles in the lack 

 of a vertebrarterial canal and in the relative widths of the 

 anterior and posterior facets. 

 The dimensions of the atlas are: 



Millimeters 



Total width 320 



Width across atlar-occipital facets 204 



Width across atlar-axis facets 255 



The axis. — The axis is a massive bone with a high neural 

 arch, the spine being an equilateral triangle in midsection. On 

 its posterior face a shallow groove arises between the zygsk- 

 pophyses which fades out about two-thirds of the -wsiY to the 

 summit. The prezygapophyses overhang the atlas in front 

 but present no articular facets. The odontoid process is a 

 truncated cone and is not so prominent relatively as in 

 Palaeosyops, being about one-third the length of the centrum 

 measured along its inferior face. The latter exhibits a low 

 longitudinal ridge below but is not deeply excavated on either 

 side, as in Palaeosyops. The transverse processes of the speci- 

 men are broken away, but the bases of its two supports are 

 seen, indicating the position of the vertebrarterial canal, which 

 is placed rather high on the centrum, though not on a line 

 with its upper surface, as is Palaeosyops. 



The postzygapophyses look downward and outward; their 

 horizontal axes, if continued, would intersect at an angle of 

 90°. Altogether both atlas and axis resemble those of a 

 rhinoceros, much more than those of Palaeosyops. 

 The measurements of the axis are as follows: 



Millimeters 



Total height to summit of spine 295 



Greatest breadth 241 



Length of centrum including odontoid 133 



The remaining cervicals are distinctly opisthocoelous, with 

 zygapophyses which widely overlap one another. With the 

 exception of the sixth, they are quite poorly preserved, and the 

 sixth is so badly crushed as to make measurements very 

 unreliable. 



Of the dorsals, nine only are referable to the type specimen, 

 though three others are added in the mount. The opistho- 

 coelous centra are preserved, but the spines and transverse 

 processes are lacking. 



The ribs. — Portions of thirteen ribs from both sides of the 

 body are preserved. In general form they are quite rhinoceros- 

 like, being somewhat widely expanded in the shaft. The 

 capitulum is nearly spherical in most of the ribs preserved, and 

 the two facets are separated from each other by a deep groove. 

 In an anterior rib, the second or third, the tubercular facet, 

 while mainl}' on the posterior side, arches over so as to lie in 

 part on the anterior face. The other ribs have the tubercular 

 facet entirely on the posterior face. The resemblances again 

 are with the rhinoceros rather than with Palaeosyops. 



•' Earle, Charles, Acad. Nat. Sci. Philadelphia Jour., 2d ser., vol. 9, p. 294, 1892 



