172 THE CEKATOPSIA. 



RELATIONSHIP OF SPECIES. 



If one were to group the species of Triceratops according to affinities the result would be 

 expressed something as follows: 



Group 1. Group 2. 



T. horridus. T. elatus. 



T. prorsus. T. calicornis. 

 T. brevicornus. 



T. serratus and T. flabellatus would each stand alone, although in some features they 

 suggest each other. 



Of the species alticornis, sulcatus, and obtusus the skulls are too fragmentary for a fair 

 comparison. T. obtusus, because of its greatly reduced nasal horn, and alticornis, from the 

 development of the long, slender supraorbitals, seem to be the most specialized. 



II. THE CERATOPS-TOROSAURUS PHYLUM. 

 CERATOPS. 



Of the four species mentioned under this genus in the alphabetical list on pages 11-12, two, 

 C. (Bison) alticornis and C horridus, have been removed to the genus Triceratops , with which 

 their affinities clearly lie, and one, C. (Hadrosaurus) paucidens (pp. 103-104), is of question- 

 able validity, for, as Hatcher says: 



It is not at all unlikely that the type of the present species [a maxillary and premaxillary] pertained to one of the several 

 species of Ceratopsida? already described as from the Judith River beds. Since, however, the teeth, the maxillaries, and the pre- 

 maxillaries of all these are imperfectly known, it is at present impossible to determine to which of them this specimen should 

 be referred. 



Thus there remains of the original four but one, the type species G. montanus, to which 

 Hatcher has added three which he removed from the genus Monoclonius. 

 The list of species as revised by Hatcher is as follows: 



1. Ceratops montanus Marsh. Type. 



2. Ceratops canadensis Lambe. 



3. Ceratops recurvicorniso. Cope. 



4. Ceratops belli Lambe. 



1 . Ceratops montanus Marsh (pp. 1 00-1 02 , figs. 1 03 and 1 04) , the type species, is based upon an 

 occipital condyle and a pair of supraorbital horn cores, No. 2411, National Museum. 



The supraorbital horn cores were of moderate length, subtriangular in section at the base, 

 but nearly circular in the upper half. They are not compressed, but curve strongly outward and 

 slightly forward. The frill is unfortunately unknown in the type species. 



2. Ceratops (Monoclonius) canadensis Lambe (pp. 93-96, figs. 96, 97, Pis. XVIII, XIX, 

 XXIII) is known from portions of a skull and an anterior dorsal (No. 1254 a, b, c, d, e of the 

 Canadian Geological Survey). Hatcher removed this species from the genus Monoclonius 

 because of the similarity of the supraorbital horn core with that of the type species of the 

 present genus. He does not, however, give us his final decision as to whether it is to be con- 

 sidered specifically distinct from C. montanus or not, as that point was left for the present 

 discussion, which Hatcher unfortunately did not live to undertake. 



The only distinction must lie in the character of the supraorbital horn cores, which, although 

 Hatcher considers them "essentially the same," seem to differ in that the base is subtriangular 

 in section in C. montanus and circular in C. canadensis. Another distinction lies in the curvature 

 of the horn. In canadensis the horns curve well forward, then upward, but in montanus they are 

 more nearly straight and, if Hatcher's arrangement expressed in fig. 103 is correct, flare outward 

 strongly in a most peculiar manner. 



The nasal horn core was lost before f ossilization, as the creature was young, so that its char- 

 acters can not be determined. 



" The present writer questions the reference ol recurvicornis to this series for the reasons given on page 173. 



