DISCOVERY OF THE TITANOTHERES AND ORIGINAL DESCRIPTIONS 



217 



Fixation of ledotype. — Cope's conclusion that the 

 above-mentioned fragments "are probably without 

 admixture" appears open to doubt. The "frontal 

 tuberosity" referred to is shown by comparison with 

 well-preserved material to be the horn core of the left 

 side of an immature individual resembling Allops 

 marshi, a reference favored by Cope's observation of 

 the wide bridge over the infraorbital foramen, which 

 contrasts with the narrow columnar bridge in Bron- 

 totheriwn and Symhorodon. The oval-sectioned horn 

 core which Cope supposed to be borne on the nasals is 

 a right horn core of very different shape, agreeing closely 

 with that in skull No. 4702, U. S. National Museum, 

 which Osborn selected (1902.208, p. 106) as the neo- 

 type of this species. The oval-sectioned horn core 

 may, therefore, be regarded as the ledotype. 



Etymology. — invb, below; /cepas, horn; in allusion to 

 the supposed presence of a low horn swelling on the 

 frontal, behind the one on the nasal. 



Present determination. — As thus interpreted, hypo- 

 ceras is a valid species of the genus BrontotJierium. 



Anisacodon Marsh, 1875 

 Cf. Menodus, this monograph, page 522 



Original reference. — Am. Jour. Sci., 3d ser., vol. 9, 

 p. 246, March, 1875 (Marsh, 1875.1). 



Type species. — Anisacodon montanus Marsh (see 

 below). 



Generic characters (Marsh). — "Dentition: Incisors-?; 

 canines y; premolars f ; molars f. No superior dias- 

 tema. Strong inner basal ridge on upper pre- 

 molars. Last upper molar with two inner cones. No 

 postorbital process." 



Etymology. — iivtcT-os, unequal; (xktj, point; 66ous, 

 tooth. Possibly in allusion to the unequal develop- 

 ment of the two inner cones on the third upper molar. 



Present determination. — In view of the strong 

 similarities to Menodus in the vestigial condition of 

 the incisors, in the strong internal cingulum in the 

 premolars, in the shape of the nasals, and in the second 

 internal cone of the third molar, this genus is now 

 regarded as a synonym of Menodus. 



Anisacodon montanus Marsh, 1875 

 Cf. Menodus giganteus?, this monograph, page 537 



Original reference. — ^Am. Jour. Sci., 3d ser., vol. 9, 

 p. 246, March, 1875 (Marsh, 1875.1). 



Type locality and geologic horizon. — "Northern 

 Nebraska" (Big Badlands, White River, S. Dak.); 

 Chadron formation {Titanotherium zone); exact local- 

 ity and level not recorded. 



Type. — A fragmentary skull including the maxil- 

 laries and fragmentary molar teeth. Yale Mus. 

 10022. (See fig. 175.) 



Specific characters. ^Mursh. writes: 



This species is especially distinguished by the emargination 

 of the extremity of the nasals, the short premaxillaries, and 

 101959— 29— VOL 1 17 



the rectangular form of the last upper molar. The inner pos- 

 terior cone of this molar is smaller than the one in front, and 

 quite distinct from the posterior basal ridge. 



Measurements [selected from Marsh] 



Millimeters 



Width of nasals above end of premaxillaries 95 



Anteroposterior diameter of last upper premolar 43 



Anteroposterior diameter of penultimate upper molar 77 



Anteroposterior diameter of last upper molar 84 



Etymology. — montanus, dwelling in the mountains. 

 Exact allusion uncertain, unless the badland topogra- 

 phy of South Dakota is thought of as mountainous. 



\ 



Figure 172. — Type (holotype) skviH of Sy7nborodontrigonoceras 

 Am. Mus. 6355. One-ninth natural size. 



Present determination. — In the form of its premolars 

 and third molar as well as in its vestigial incisors this 

 animal resembles Menodus giganteus; the emarginate 

 nasals with processes on either side of the median 

 notch also recall female Menodus skulls. Anisacodon 

 (Diconodon) montanus is probably referable to Meno- 

 dus cf. M. giganteus. 



"Diconodon non Anisacodon" Marsh, 1876 



Cf. Menodus giganteus, this monograph, page 530 



Original reference. — Am. Jour. Sci., 3d ser., vol. 11, 

 p. 339, April, 1876 (Marsh, 1876.1). In this paper 

 Marsh gives diagnosis of four genera of Brontothe- 

 ridae. No. 4 is called "Diconodon Marsh (Anisaco- 



