MONOCLONIUS. 71 



Monoclonius ceassus Cope. 1876. 



Type (No. 399S, American Museum of Natural History) consists of teeth?, sacrum, anterior dorsals, and parietal. 



Original description in Proc. Acad. Nat Sci. Phila., vol. 28, 1876, pp. 25.5-256. 

 Cope, E. D., Bull. U. S. Geol. and Geog. Surv. Terr., vol. 3, 1877, pp. 573, 594; Am. Naturalist, vol. 14, 1880, p. 511; ibid., 



vol. 20, pp. 153-154; vol. 23, 1889, pp. 71.5-717, 905. 

 Lambe, L. M., Contr. to Canadian Pal., vol. 3 (quarto), pt. 2, 1902, p. 68. 

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

 Osborn, F. H., Contr. to Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 14, 20. 



ORIGINAL DESCRIPTION. 



Cope's original definition of this genus and species was as follows: 



Char. gen. — Teeth with obliquely truncate face and distinct root, which is grooved for the successional tooth on the front. 

 No external cementum layer, caudal vertebne biconcave, and brim narrow. Fore limbs large and massive. 



The teeth of this genus resemble those of Hadrosaurus, and like them are replaced from the "front," an arrangement 

 which precludes the possibility of more than one series of teeth being in functional use at one time. The robust fore limbs 

 and elongate ilium distinguish Diclonius a from Hadrosaurus. From Trachodon it differs in the absence of the rough cementum 

 layer on the back of the tooth. 



Char, specif. — The faces of the teeth are acuminate oval in form and are divided by an elevated keel, which is median 

 above, but turns to one side at the base. Margin crenate, the grooves extending more or less on the crown " back," which 

 is otherwise smooth. 



Sacrum with ten vertebra, the last centrum much compressed, the diapophyses extending horizontally from the neural 

 arch above, and connected by a vertical lamina with the iliac supports; length, 27.33 inches. The bones of the limbs are 

 robust, the hinder the longer, but not so much so as in some other genera. Length of femur, 22 inches; width, proximally, 

 7.4 inches; distally, 6 inches. Length of tibia, 20 inches; greatest diameter, proximally, 8 inches; distally, 7.25 inches. 

 The three anterior dorsal vertebrse are coossified, and the first exibits a deep cup for articulation with the preceding vertebra. 

 The episternum is a T-shaped bone, thin and keeled on the median line below. Length of transverse portion, 21 inches. 



Subsequent discoveries have shown that the above description is erroneous in many par- 

 ticulars. First, Cope's description of the teeth seems to have been based, not on the teeth of 

 Monoclonius, but on those of Trachodon, since he says that they resemble those of Hadrosaurus 

 and are replaced in a similar manner from in "front," while we now know that they differ 

 from the teeth of both Hadrosaurus and Trachodon in that they are fixed in the jaw by two roots 

 inserted transversely instead of by one root, as in both the latter genera, and that they are 

 replaced from below in much the same maimer as the deciduous teeth are replaced by the 

 permanent set in the Mammalia; second, the statement that "the three anterior dorsal verte- 

 bras are coossified" has been shown by subsequent discoveries to apply to the three [four] 6 

 anterior cervicals, Cope having mistaken the cervicals for dorsals; third, the T-shaped bone, 

 described as an episternum, we now know to be the coossified parietals. 



Notwithstanding these errors, which, owing to the pioneer nature of the work and the 

 rather fragmentary material upon which it was based, we may excuse, the size and form of the 

 parietals, squamosals, and supraorbital horn cores and the characters of the sacrum and the 

 relative proportions of the fore and hind limbs, as described by Cope, may be -considered as 

 fairly diagnostic of the genus and as placing it on a valid foundation, while little difficulty will 

 be found in identifying the species (M. crassus), either from the original and subsequent descrip- 

 tions by Professor Cope or from actual comparisons of other material with that of the type, 

 which latter method should always be the final course of arbitration in determining the 

 synonymy of all closely related and apparently identical forms. 



LITERATURE. 



In 1886 c Cope described and figured as a probable sternal element the parietal of Mono- 

 clonius crassus, and discussed at some length the structure of the sternum in the Dinosauria. 



Two years later/ after Professor Marsh had described and figured the type of Ceratops 

 montanus, Cope identified as a frontal horn core the elem ent figured by him in 1877/ He al so 



a This is certainly a misprint. Cope undoubtedly meant to say Monoclonius. See also Proc. Acad. Nat. Sci. Phila., 1S83, p. 100. 



b See footnote on p. 76. 



c Am. Naturalist, vol. 20, Feb., 1886, pp. 153-155. 



d Am. Naturalist, vol. 22, Dec, 1888, pp. 1108-1109. 



«P1. 34, fig. 8, Bull. U. S. Geol. and Geog. Surv. Terr. 



