GENERIC AND SPECIFIC SUMMARY. 167 



REVISION OF SPECIES. 



I. THE MONOCLONIUS-TRICERATOPS PHYLUM. 

 MONOCLONITJS. 



Of the seven species referred to the genus Monoclonius by their several authors, Hatcher 

 retains but three, M. crassus Cope, M. dawsoni Lambe, and M. sphenocerus Cope. He abandons 

 M. fissus Cope, because of insufficient type material, while the remaining three, canadensis 

 Lambe, recurvicornis Cope, and belli Lambe, are removed to the genus Ceratops. 



1. Monoclonius crassus Cope (pp. 71-80, figs. 75-88) is the type species and is known from 

 the remains of at least two individuals (type No. 3998, American Museum of Natural History), 

 including the parietals, the frontal and postfrontal bones, a supraorbital horn core, and other 

 portions of the skeleton. Of this material only that pertaining to the skull can be used in 

 specific contrast, for of the remaining species no skeletal parts are known. 



The supraorbital horn core (fig. 76) is low, broad below, and pointed above, with a flat outer 

 face and a strongly convex inner surface. The main point of contrast with that of M. dawsoni 

 seems to be one of size, as in the latter the horn cores are extremely diminutive, so small, 

 indeed, as to have been overlooked by so careful an observer as Lambe. The orbit is nearly 

 circular, with a thick, rugose border. 



The complete parietals (fig. 75) are known only in this species, though fragments of parie- 

 tals included in the type specimen of M. dawsoni show no specific distinctions from those of the 

 species under consideration. 



As the parts preserved in M. crassus are unknown in M. sphenocerus one can not contrast 

 them. 



2. Monoclonius dawsoni Lambe (pp. 89-93, fig. 92) is known from cranial fragments of 

 specimen No. 1173, Geological Survey, Canada. The second specimen, consisting of parietals 

 and a nasal horn core (No. 971), referred to by Lambe in his original description, has been made 

 the type of a new genus and species, Centrosaurus apertus Lambe, in a paper published" since 

 Hatcher's death (see p. 93, footnote b). 



The nasal horn core is large, somewhat compressed, backward curving, and ovate in section, 

 with the broader end in front, differing materially in shape from that of M. sphenocerus. The 

 supraorbital horns are described as very diminutive and triangular in section, as in M. crassus. 

 About 1 inch of the apex is not preserved. 



The parietals are known only from a fragment with four marginal undulations, as in M. 

 crassus. 



The orbit is large and circular. Both orbit and nasal horn core are xevj large in proportion 

 to the occipital condyle, maxillaries, and quadrate. Hatcher was "inclined to regard the 

 present species as closely allied to if not identical with M. crassus of Cope." Some of the 

 remainder of the material provisionally associated with the type by Lambe, consisting of a 

 sacrum, a scapula and coracoid, a predentary, and a rostral bone, may pertain to other genera 

 and species. 



3. Monoclonius sphenocerus Cope (pp. 87-88, fig. 91, A, B, C) consists of portions of pre- 

 maxillary, nasals, and nasal horn of a large though scarcely adult animal. It is distinguished 

 from M. dawsoni in the form of the nasal horn, which is much compressed, with the anterior 

 margin acute and the posterior rounded, the reverse of that of the last-mentioned species. In 

 M. sphenocerus the horn is straight and directed upward and backward instead of being curved 

 backward, as in M. dawsoni. It is, as Hatcher says, the largest and most powerful nasal horn 

 core observed in any of the Ceratopsidae (fig. 91). Thus M. sphenocerus is in sharp contrast 

 with M. dawsoni, and probably also with M. crassus, though a direct comparison with the latter 

 can not be made. The nasal horn resembles most closely the one associated by Lambe with 

 the parietals which constitute the type of his new genus Centrosaurus, and the true affinities of 

 M. sphenocerus may prove to lie with that genus. 



" Ottawa Naturalist, vol. 18, 1904, pp. 81-84. This paper was issued July 7, tour days after Hatcher's death. 



