DYSGANUS. 69 



Dysganus peiganus Cope. 1876. 



Type (No. 3974, 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 Kozlonj 7 , Budapest, 1901, vol. 31, p. 270. 

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



In the typical tooth of this species the form approaches the genus Palieoscincus Leidy, in the compression of the crown 

 and the contraction of the base; it is a limital species of Dysganus if really properly placed in that genus. 



The widest portion of the crown is above the base; from this expansion it contracts in both directions, and in the unworn 

 tooth forms an angular median apex. This is not the case in D. encaustus, which is regularly rounded. The margin of the 

 crown is narrowed, expanding but little toward the expansion, and is quite rugose. From these rugosities low ridges descend 

 on the face of the tooth, whose surface is also minutely rugose. The face is divided by a prominent median rib, which extends 

 to the apex. No cementum is visible on the basis in the only specimen in which this part is preserved. 



Measurements. „, 



M. 



Length of crown 0. 008 



Diameter of crown, transverse . 005 



Diameter of crown, antero-posterior, at base 008 



Diameter of crown, antero-posterior, greatest 011 



From the above descriptions of this genus and the various species placed in it by Professor 

 Cope it will readily appear that he included in it teeth pertaining both to the Ceratopsidae 

 and to the Trachodontidse, while the type of D. peiganus should be considered from his descrip- 

 tion as pertaining to some member of the Stegosauridse, and perhaps not specifically different 

 from the tooth figured by Lambe on page 5? of his Vertebrate Fauna of the Mid-Cretaceous 

 of the Northwest Territory, and provisionally referred by him to Stereoceplialus tutus. 



In attempting to determine the affinities of the genus, however, we should rely chiefly upon 

 the characters presented by the types of the typical species, D. encaustus. Since, however, these 

 types are no longer available, we have to rely upon their characters, as described by Cope. If, 

 as Professor Cope has stated in his definition of the genus, in the teeth "the body of the crown 

 is a flattened shaft of dentine " and "the crowns are compressed, so that the fore-and-aft diameter 

 much exceeds the transverse," then these teeth can not pertain to the Ceratopsia, for in no 

 member of that group known to the present writer have the teeth either the form or the propor- 

 tionate diameters given by Cope. Neither am I acquainted with any species of the Ceratop- 

 sidse in which there are no crenulations on the margins of either the worn or unworn teeth, as 

 is stated to be their condition by Cope in D. encaustus, the type species. Neither does the 

 method of replacement of the teeth in any of the Ceratopsidse resemble that of Cionodon, as the 

 latter has been described by Cope on page 448 of his Report on the Vertebrate Paleontology 

 of Colorado, which is as follows: 



The teeth are rod-like, the upper portion subcylindric in section, with the inner face flattened from apex to base, while 

 the lower half is flattened externally by an abrupt excavation to the middle for the accommodation of the crown of the suc- 

 cessional tooth. The inner face of the tooth, from apex to base, is shielded by a plate of enamel, which is somewhat elevated 

 at the margins and supports a keel in the middle, thus giving rise to two shallow longitudinal troughs. The remainder 

 of the tooth is covered with a layer of some dense substance, possibty cementum, which overlaps the vanishing margins of the 

 enamel. The outer inferior excavation of the shaft presents a median longitudinal groove to accommodate the keel of the 

 closely appressed crown of the successional tooth. The apex of the tooth being obtusely wedge-shaped, the functional tooth 

 is pushed downward and transversely toward the inner side of the jaw. The tooth slides downward in a closely fitting vertical 

 groove of the outer alveolar wall. The inner wall is oblique, its section forming, with that of the outer, a V; it is furrowed 

 with grooves similar and opposite to those of the cuter wall, but entirely disconnected from them. The base of the shank of 

 the functional tooth, on being displaced by the successional, slides downward and inward along the groove of the inner side, 

 each lateral movement being accompanied by a corresponding protrusion. At the most, three teeth form a transverse line, 

 namely, one new apex external, one half-worn crown median, and the stump or basis of a shank on the inner. The new 

 crowns are, however, protruded successively in series of three, in the longitudinal direction also. Thus, when an apex is freshly 

 protruded, the shank in front of it is a little more prominent, and the third stands beyond the alveolar border. As each shank 

 increases somewhat in diameter downward in the C. arctatus, the section increases in size with protrusion; hence, before the 

 appearance of a new crown outside of it, there are but two new functional teeth in a cross row. Thus, in the outer longitu- 

 dinal row, only every third tooth is in functional use at one time; in the middle series all are in use, while in the inner, every 

 third one is simultaneously thrown out in the form of a minute stump of the shank, if not entirely ground up. 



