13 



robust, and the external columns are prominent; the intervening spaces 

 are impressed, and have a distinct median ridge. Enamel smooth or 

 slightly rugose at base of crown . 



Measurements. M. 



Length of two superior molars .030 



t-.. , f r, . . , f anteroposterior 015 



Diameter of first superior molar-; I 



v. transverse 017 



These dimensions are those of the A. equiceps. 



Anchithebium longicristis, sp. nov. 



This is a smaller species than the two above described, having the di- 

 mensions of the A. bairdi. The best specimen representing it consists of 

 a right maxillary bone, which supports all the molars excepting the last. 

 The infraorbital foramen issues above the third premolar. The first pre- 

 molar is two- rooted ; the second is not elongate, and is equal to the other 

 premolars, or the penultimate true molar, in antero- posterior diameter. 

 There are no interior basal tubercles or cingula, but the anterior cingulum 

 has a tubercle which is appressed closely to the anterior median. The 

 posterior cingulum expands into a large trihedral posterior marginal tuber- 

 cle. The anterior median tubercle- crest, appears in the worn state to be 

 moderately distinct from the internal ; both it and the posterior middle are 

 characterized by their production outwards ; the latter passing between the 

 exterior crescents and forming a junction with their common connection. 

 The external cingula are not strongly marked, nor the external faces of 

 the crescents impressed ; the latter are convex, and with the median ridge 

 little distinct. Enamel smooth. 



Measurements. M. 



Length of anterior six molars 062 



" premolar series . 044 



Diameter of second premolar { anteroposterior 013 



(- transverse 014 



Diameter of second true molar I anteroposterior 0125 



*. transverse 0165 



In the Annual Report of the U. S. Geol. Surv. Terrs, for 1873,* I gave 

 the comparative characters of the three species of this genus then known 

 to me, viz. : A. bairdi Leidy ; A. cuneatum Cope, and A. exoletum Cope. 

 I now give a table in which the three species above described are intro- 

 duced, with the A. condoni Leidy. 



A A tubercle between the internal lobes of the superior molars. 

 Larger ; median tubercles well separated ; large anterior and posterior 



marginal tubercles .A. equiceps. 



Smaller; median tubercles not separated ; no anterior marginal and a small 



posterior marginal tubercle A. bairdi. 



A A No tubercle between inner lobes. 

 * Paste 496. 



