Measurements. m. 



Length of basis of tooth 012 



■ i anteroposterior 009 



Diameter of crown | trangverse 0Q4 



Transverse diameter below crown 008 



The teeth are rather smaller than those of Hadrosaurus foulkei, 

 The borders present no indication of the crenation seen in that 

 and other species, either in worn or unworn specimens. 



Dysganus haydenianns, nov. sp. 



Represented by a number of teeth found in such relation that 

 they are supposed to belong to two individuals. 



They differ materially in form from those of the D. encaustus, 

 and exceed any of them in size. 



The base of the tooth possesses the thick investment of rough 

 cementum, and has a slope away from the base of the crown. The 

 form of the crown is peculiar in possessing a lateral face placed 

 at a strong angle to the usual face, and separated from it by a 

 strong protuberant angular ridge. This angular cutting face would 

 resemble that of the Diclonii were it not that the body of dentine 

 of which it is composed is a flat plate instead of a triangular seg- 

 ment of a subquadrate prism. Each face has a separate plate, 

 which is separated from the other by a suture. A solid mass fills 

 the angle between them, which is divided by a groove produced 

 by the pressure of the angle of the face of the succeeding tooth 

 which fits it. The wider of the "front" faces is divided by a low 

 longitudinal ridge. Both of the faces are bounded by an external 

 incurved ridge which cause them to have a concave surface. 



A tooth of a size equal to that of the one just described was 

 found with it, has a form more nearly like that of D. encaustus, in 

 the less degree of prominence of the lateral angle. It displays but 

 a single posterior cementum-like mass, which presents considerable 

 lateral faces as well as a posterior one, as in the first described 

 tooth. 



Measurements. m. 



Length of base of crown 010 



Elevation of remaining part of crown 006 



! anteroposterior 015 

 transverse, total 010 

 " dentine . . . .004 



Dedicated to Doctor F. V. Hayden, U. S. Geologist. 



