1878.] < 5 [Cope. 



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. 



Measiorements. M. 



Length of two superior molars 030 



t-.. . e *. . . , f antero-posterior 015 



Diameter of first superior molar \ * 



<- transverse 01 1 



These dimensions are those of the A. equiceps. 



Anchitheridm 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 anteroposterior 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 002 



" premolar series 044 



t\- > e i i ( antero-posterior 013 



Diameter of second premolar^ * 



t transverse 014 



t\- * e t * i f antero-posterior 0125 



Diameter oi second true molar * 



t 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. < quiet pa. 



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



posterior marginal tubercle A. bairdi. 



A A No tubercle between inner lobes. 

 * Page 196. 



