27(i Annals of the Carnegie Museum. 



maintain that the second inferior incisor of Trigonias oshorni from the 

 lower Oligocene has already become hypertrophied into a large pro- 

 cumbent cutting tooth while immediately behind it is placed the ca- 

 nine. Quite recently there has appeared a paper on Diceratherium 

 by Loomis in which this large procumbent tooth is again referred to 

 as the lower canine (/. c, p. 52). From the material now at hand it is 

 possible not only to substantiate the contention of Lucas and Hatcher 

 but entirely to establish as a fact that the upper incisor of the Rhino- 

 cerotidcc does not oppose the loiver canines but opposes the lower incisor 

 two or three. The deciduous incisor dentition as well as the canine of 

 the lower jaw in Diceratherium is complete. The second or third 

 permanent incisor has entirely taken up the space of lo and 3, while 

 at some distance behind the canine occurs In adult forms all evidence 

 of the canine is entirely obliterated. When the earlier Tertiary 

 ancestors of the Rhinocerotidae are found the lower canine will 

 undoubtedly be found to be much more reduced in size than the 

 upper, while 1 9^ or I ^^ will be found to oppose the enlarged upper incisor 



Vertebral Column. 

 Cervicals,'/; Dorsals, io{?); Lumbar s, j{; Sacrals, 4-5; Caudals, 26 {?)■ 

 The cervical vertebrae are comparatively short and heavy. The 

 axis has a strong overhanging neural spine, the third cervical lacks 

 the spine, while the fourth has it only faintly indicated. On the suc- 

 ceeding three cervicals the increase in length of the neural spines is 

 more rapid, the seventh being of considerable height. Nineteen 

 dorsals are inserted in this skeleton which is thought to be approxi- 

 mately correct inasmuch as certain species in the ancestral line from 

 the upper Oligocene {Aceratherium tridactylum^) have this number. 

 The anterior dorsals have short, broad, and depressed centra, and high 

 and heavy neural spines. Further back the centra are higher, nar- 

 rower, and terminate ventrally in more defined keels, while the neural 

 spines are lighter and lower; the five or six last dorsals already as- 

 suming the lumbar-like neural spines. There are five lumbar vertebrae 

 in A. tridactylum which is also true of the present form. The sacrum 

 on the other hand is composed of from four to five coossified vertebrae, 

 while in the Oligocene form there are three (Osborn, /. c, p. 85). A 

 series of caudals, seventeen in number, are of one individual (No. 

 1843) found in consecutive order from the first to the seventeenth. 

 sOsborn, H. F., Bull. Am. Mas. Nat. Hist., VoL V. p. 85. 1893. 



