APtT. XXXIII.-OX A CARNIVOROUS DINOSAURIAN FROM THE 

 DAKOTA BEDS OF COLORADO. 



By E. D. Cope. 



The vertebrate fauna of the Dakota epocli of the regions west of the 

 Mississippi having been heretofore unknown, it is satisfactory to be able 

 to state that I h ave recently received, from a new locality, evidence of 

 the existence of some colossal species of JDinosauria during this period'. 

 This is derived from a skeleton discovered near to the town of Canyon 

 City, on the Arkansas Eiver, near the point where the latter issues from 

 the caiion through the Greenhorn Eauge of the Eocky Mountains. 



At present, I only describe a portion of the right dentary bone, which 

 supports eight teeth, and contains a cavity at the anterior extremity, 

 from -which one tooth was probably shed* The dentition is of the car- 

 nivorous type, and does not differ from that of the species of the genus 

 L(claj)s, to which have been referred numerous species from Cretaceous 

 Xos. 5 and 6. The crowns exhibit the gradua^modiflcation of form in 

 the succession from rear to front which I have already described in the 

 Laiaps incrassatiis.* There are subordinate characters exhibited by the 

 present animal which show that it is quite distinct from any of the spe- 

 cies heretofore known. 



Five successional and two functional teeth exhibit crowns complete, 

 or nearly so. The posterior exhibit a nearly straight posterior edge and 

 an anterior one curved backward to a subacute erect apex. Both are 

 denticulated, but the denticles of the anterior edge do not descend so 

 near to the base of the crown as those of the posterior. The anterior 

 series turns inward toward the base. The section of the crown is here 

 (at ihe ninth tooth from before) not quite symmetrical, the internal 

 face being the more convex near the apex. Soon the greater convexity 

 of the outer side of the crown near the base becomes apparent, and as 

 the inward curvature of the anterior denticulate edge increases, the con- 

 vexity becomes more pronounced. On the second tooth, which is the 

 first one preserved, the posterior edge is median ; the anterior edge is 

 on the inner side of a gently convex anterior face, which passes into the 

 external face by an abrupt convexity. The long axis of the section of 

 thecrown does notconnectthe cuttingedges, but passes from the posterior 

 edge to the extero-anterior convexity mentioned, and parallel to the sym- 

 physis mandibuli. The enamel is smooth and with a fine silky luster. 

 Two stages of succession are evident in these teetli. Successional crowns 



5 BULL 



See Proceedings Academy Phila., Jauuary, 1S77. 



605 



