234 BULLETIN UNJTElJ .STA'J'K.S (ilAjlAJdiCAL HCliVKV. \VoLV. 



I'wo S])CcicK of tlii.s genus firo known to me, on(5 of wliicli lia.s boon 

 found in tlic Wliitc Jfiver Ixids of Colorudo, and the other in tlio corre- 

 Hponding horizon in Oregon, vi/ : tlie A. fptadripUeatus and the A. tuhifer. 



Without fuller material it i.s not easy to determine the near affinities 

 of Anclmodon. Wliile the identity of the forms of some of the premo- 

 hir and molar teeth i.s much as in the RJdnoceridw, and distijiguishes the 

 genus from Lophiodon, Ifyrachyits, ete., tlui details of the inolars ai-e 

 more like those of the latter genera. The elongation of the second pre- 

 molars have, on the other hand, a i)oiiit of similarity to the Anchitheroid 

 forms. 



HYIIACODON Leidy. 



Pro(;c(Mlirif^H of tlic Ao,a<l('iny f)f N.'itiira] ,S(uctk;(;h, riiiljiddlpliia, 1850, j). 'J2; lb57, p. 

 8'J; Extinct FiHinu Dakota and Nebraska, p. 2'.'>2. 



I'rofessor Leidy has i>ublished the dental and several cranial charac- 

 ters of this genus, so that there remain hut f(;w of these to he observed. 

 Professor Marsh has stated the number of the toes,* and I will add 

 some points not noticed by either of these paleontologists. 



The dental formula is I. f ; C. |; Pm. f ; M. f. The incisors and 

 canines form uninterru2)ted series in both jaws, win'ch are separated by 

 diastemata from the molar series. In their unwoni condition, the crowns 

 of the incisors and (canines ai-e subconi(;. The molars of both jaws do 

 not differ in character from those oi Accratherium, but the last superior 

 molar differs in not having the i)Osterior cross-crest confounded with the 

 external wall. 



According to Leidy, the x>i'emaxillary bone reaches the base of the 

 nasal. The tem])orid fossai are large; and approach each other above. A 

 (character heretofore unnoticed is the ai)i)earance of the mastoid bone 

 between the posttympanic and the paroccipital i)roce8se8, as in horses, 

 thus differing fiom rhinoceroses. As in Aceratherium, the posttym- 

 panic does not close the meatus auditorius inferiorly. Postglenoid well 

 developed. This genus also differs from the rhinoceroses in the absence 

 of the tuberosity Ijehind the condyle of the lower jaw. 



The vertebral column is characterized by the length of the cxjrvical 

 jwrtion as compared with the dorsal, especially of the axis. The ver- 

 tebrarterial canal is long and external ; the centra are keeled below, 

 and the transverse processes of the atlas are not elongate. The opis- 

 thocoilous character is well marked in both cervical and dorsal centra. 

 The zyga,i)ophysial facets of the dorsals are not recurved in any way, 

 and there are some metapophyses on the posterior dorsals. There are 

 no enclosed spinal i'oramina on tlui dorsals. Lrnnbars unknown. 



A single species of this geiuis, the JL nchrascemis, was found by llay- 

 den in Nebraska, and I obtained in Colorado in 1873 a second one, the 

 if. arcidcns. 



*Amor. Jonru. Soi. ArtH, 1877, p. 3G1. 



