DISCOVERY OF THE TITANOTHERES AND ORIGINAL DESCRIPTIONS 



207 



possess a remarkably strong basal ridge and indicate an animal 

 larger than any species of existing Rhinoceros; the greatest 

 transverse diameter of the third premolar being 2J^ inches; 

 its anteroposterior diameter 1% inches. For the species the 

 name Rhinoceros americanus is proposed. 



Etymology. — americanus, in allusion to the then 

 novel fact that a supposed rhinoceros had once in- 

 habited America. 



Present determination. — It does not seem possible 

 to determine positively whether these isolated pre- 

 molar teeth belong to Allops or to Menodus; the 

 affinity to one or the other of these genera is indicated 

 by the pronounced internal and external cingula and 

 by the large tetartocone on p*. In view of the doubt 

 and the disappearance of the type, it seems best to re- 

 gard "Rhinoceros" americanus as indeterminate. 



Eotherium Leidy, 1853 



Cf. Menodus Pome!, this monograph, page 522 

 Original reference. — Acad. Nat. Sci. Philadelphia 

 Proc, vol. 6, p. 392, 1853 (Leidy, 1853.1). 



Present determination. — The specimens indicated 

 were first chosen the types of Rhinoceros americanus. 

 (See above.) The very pronounced internal and 

 external cingula of the type (fig. 162), however, 

 appear to indicate that they belong generically to 

 Menodus. The genus Eotherium was subsequently 

 treated by Leidy as a synonym of Titanotherium. The 

 name Eotherium was subsequently (1875) applied by 

 Owen to a genus of sirenians. 



Palaeotherium giganteum Leidy, 1854 



(Indeterminate) 



Original reference. — The ancient fauna of Nebraska: 

 Smithsonian Contr. Knowledge, vol. 6, p. 78, pi. 17, 

 figs. 11-13, 1853 (Leidy, 1854.1). 



Type locality. — White River, "Nebraska" [South 

 Dakota]. 



Types. — Portions of the ectoloph of five molars "in 

 the collections of Mr. Culbertson and Dr. Owen." 



Lectotypes (Osborn). — The fragmentary ectoloph 

 figured in Plate 17, Figure 11, of Leidy's work. (See 

 fig. 163.) 



Figure 163. — Cotypes of Palaeotherium giganteum 

 Parts of the ectoloph of upper molars. After Leidy, 1853. Natural size. 



Subsequent reference. — Leidy, The ancient fauna of 

 Nebraska, pi. 17, figs. 1-7, 1853 (Leidy, 1854.1). 



Type species (monotypic). — Rhinoceros americanus 

 Leidy. (See above.) 



Generic description. — Leidy says: 



Of the huge Titanotherium proutii there are numerous small 

 fragments of bones and teeth and also several entire superior 

 molars, which have served to remove some of the obscurity 

 in regard to the characters of the animal. From the last- 

 mentioned specimens it appears that those which have been 

 described as probably indicating a new species of Palaeotherium^ 

 under the name P. giganteum (Ancient fauna of Nebraska, pi. 

 17, figs. 11-13), belong to Titanotherium ■proutii, while several 

 superior molars (ib., figs. 1-7), attributed to the latter, belong 

 to a new genus associating characters of Rhinoceros and Palaeo- 

 therium. For this genus and species, represented by Figures 

 1-7, Plate 17, in the Ancient fauna of Nebraska, I propose the 

 name of Eotherium americanum. 



Etymology. — rjois, dawn, dripiov, beast; possibly in 

 allusion to the relatively early geologic age of the 

 animal. 



Characters. — Leidy writes: 



The fragments, of which there are five, are only single ex- 

 ternal lobes of the upper molars. These, externally, correspond 

 to the description of Cuvier of the teeth of Palaeotherium. A 

 conjoined pair of the lobes, forming the outer part of a tooth, 

 "present the external face strongly inclined inward in descend- 

 ing and divided by three salient ridges into two concavities, 

 which are rounded toward the fangs and terminate in a tri- 

 angular cusp at the masticating surface, the basal angles of 

 which rest upon the termination of the salient ridges." The 

 median ridge is a thick obtuse fold outward of the tooth, and 

 the anterior and posterior ridges are acute, roughened offsets 

 from the basal ridge, descending to the masticating surface. 



The measurements of the more perfect specimens are as 



follows : 



In. hnes 



Length of the longest lobe 2 4 



Length of a second specimen 2 



Breadth of the second specimen at the basal angles of the 



cusp 1 8 



Length of the shortest lobe 1 7 



Breadth of the shortest lobe at the basal angles of the 



cusp 1 3 



