68 THE CEEATOPSIA. 



the cutting face of the dentine. The latter is delicately rugose in unworn specimens. The external basal cementum rises 

 highest on the incurved border of the crown; its surface is minutely rugose, the rugosity being generally punctiform. It is 

 also of a different color from the dentine in the specimens as preserved, and is occasionally found nearly worn away. The 

 edge of unworn teeth is not serrate. 



Measurements. M 



Length of basis of tooth 0. 012 



Diameter of crown, antero-posterior . _ 009 



Diameter of crown, transverse. _ 004 



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 hatdenianus Cope. 1876. 



Type (No. 5738, American Museum of Natural History) consists of detached teeth. 



Original description in Proc. Acad. Nat. Sci. Phila., vol. 28, 1876, pp. 251-252. 

 Cope, E. D., BuD. U. S. Geol. and Geog. Surv. Terr., vol. 3, 1877, pp. 572, 594, 596. 

 Nopcsa, F. Baron, Foldtani Kozlony, Budapest, 1901, vol. 31, p. 270. 

 Osborn, H. F., Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, p. 14. 



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 the dentine of which it is composed is a flat plate instead of a triangular segment 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 causes them to have a concave surface. 



A tooth of a size equal to that of the one just described, and 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 '. 0. 010 



Elevation of remaining part of crown. _ 006 



Diameter of crown, antero-posterior . _ _ 015 



Diameter of crown, transverse, total , 010 



Diameter of crown, transverse dentine .' 004 



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



Dysganus bicarinatus Cope. 1876. 



Type (No. 3975, American Museum of Natural History) consists of detached teeth. 

 Original description in Proc. Acad. Nat. Sci. Phila., vol. 28, 1876, p. 252. 

 Cope, E. D., Bull. U. S. Geol. and Geog. Surv. Terr., vol. 3, 1877, p. 572. 

 Nopcsa, F. Baron, Foldtani Kozlony, Budapest, 1901, vol. 31, p. 270. 

 Osborn, II. F., Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, p. 14. 



This dinosaurian is represented in the collections by some of the teeth of three individuals. Two of the teeth represent 

 immature stages, while the others are worn by continued use. They all present characters not found in the D. encaustus, 

 from which they differ in a direction the opposite of that which characterizes the D. haydenianus. 



The crowns present a nearly flat face without incurved lateral angles nor prominent median keel. The basis is wide, 

 projects in a rim beyond the face, and is invested with rough cementum. The face is peculiar in being divided into three 

 planes by two low angular ridges, and its surface is smooth. The dentinal column is triangular, and there are two posterior 

 columns separated by a fissure in mature teeth. 



The absence of the lateral incurved angle and the presence of the two median ones distinguish this species from the D. 

 encaustus. 



Measurements. M 



Length of basis '. 0. 009 



Width of basis 011 



Length of worn face _ 006 



Diameter of crown, antero-posterior _ 011 



Diameter of crown, transverse 007 



