Diclonius pentagonus, Gen. et sp. nov. 



Char. Gen. — Herbivorous dinosaurians, in whicli the teeth are 

 'elongate and without distinct root, and present dense material 

 only on one side of the crown (the "front"), whose section pro- 

 duces a cutting edge. The other face of the tooth (the "back") 

 is coated with cementum, and is absorbed during the protru- 

 sion of the successional tooth from below, which thus rises from 

 " behind." In the anteroposterior direction the teeth are pro- 

 truded alternately, and the lower parts of the crowns are con- 

 tracted to give space for the apices of the adjacent young teeth. 

 In the t} 7 pe of the genus there is but a single series of teeth. 



In the known species of this genus, the dense face ("front") of 

 the crown presents a longitudinal keel, but this is not necessarily 

 a generic character. The terms "front" and "back" are not in- 

 tended to be accurate, as the faces so termed are either external 

 or internal, the direction being probably reversed in the two jaws. 



This genus is allied to Hadrosaurus and Cionodon. From the 

 former it differs in the mode of succession of the teeth, which, as 

 determined by Prof. Leidy in that genus, is from the " front" of 

 the base of the tooth, whereas, in Diclonius, the succession is as 

 in Cionodon, from the "posterior" base of the tooth. This ar- 

 rangement allows of a more continuous use of the dense face than 

 in Hadrosaurus, where that face terminates as the young crown 

 rises into functional position. A species from the Fort Union 

 bad lands of the Judith River was described b} T Dr. Leidy as Tra- 

 cliodon mirabilis. Specimens of this species from the locality 

 furnishing those of Diclonius, present the mode of succession 

 ascribed by that author to Hadrosaurus, to which genus he after- 

 wards referred the species under the name of H. mirabilis. 



The dentition of species of this genus shows that but one 

 tooth in mature functional use existed in a line transverse to the 

 axis of the jaw at one time, and that alternating with these, one 

 partially protruded crown, and one stump of a crown, present 

 masticating surfaces in transverse relation. The formula for this 

 genus should then be written 2 — 1, while in Cionodon it is 3 — 3 — 2. 



The type of this genus exhibits a mode of nutrition of the 

 young teeth similar to that seen in the genus Saurocephalus 

 among fishes. The bone is perforated by a series of foramina, 

 each of which conveyed an artery directly into the base of the 

 growing crown. 



