24 ROYAL SOCIETY OF CANADA 



will be made later. Monoclonius belli, apparently nearly related to, and 

 about one-third the size of Torosaurus gladius. Marsh, is known only 

 from the coalesced parietals of the posterior crest in which are fontanelles 

 of enormous size. M. canadensis, founded on parts of the skull, and 

 vertebrae, has double fanged teeth, small supraorbital horns and a 

 squamosal of triangular shape, scalloped on the outer edge, resembling 

 somewhat the same bone in Triceratops and Sterrholophus. M. dawsoni 

 has a large nasal horn and a broad saddle-shaped posterior crest in which 

 are fontanelles or fossœ of large size, and is probably closely related to 

 the Montana form M. crassus. The Montana species Monoclonius eras- 

 sus, M. recurvicornis, M. sphenocerus and M. fissus, and those of the 

 Belly Eiver series, M. helli, M. canadensis and M. dawsoni constitute 

 a particularly interesting and important group concerning which little 

 is as yet known, the members of which, however, are smaller and ap- 

 parently more primitive than the Laramie Ceratopsia. Professior 

 Osborn is of the opinion that " it is not at all improbable that the 

 horned dinosaurs will prove to be diphyletic, one line with persistent 

 open fossse leading from Monoclonius to Torosaurus, the other leading 

 to Triceratops with closed fossae.''^ Stegoceras validus is based on 

 portions of the skull from the median line of the head with indications 

 on the upper surface of the presence of an unpaired horn. These parts 

 were supposed to be prenasal, but, as pointed out by Fopcsa,^ they 

 probably represent the frontal and nasal elements of the sikull. In 

 Stegoceras we have an entirely new type, a unicorn dinosaur remarkable 

 in that it bore a horn springing from the fronto-nasal region, recalling 

 a somewhat similar development in the mammals Aceratherium incisi- 

 vum and Elasmotherium sibiricum. 



With the consideration of the Tracliodontidœ (duck-billed dino- 

 saurs) we reach a group of unarmed, bipedal, in many respects highly 

 specialized Predentata, of which the Belly Eiver series species are 

 Trachodon altidens, T. marginatus, T. selivyni and Cionodon stenopsis. 

 The mode of succession of the teeth in these herbivorous forms is one 

 of the most interesting characteristics of the group. T. altidens, as 

 its name implies, is distinguished from the other species by its long, 

 narrow teeth, with distinctive border sculpture. A well-preserved maxilla 

 represents this species and indicates an animal of small size. T. mar- 

 ginatum, known from excellent examples of the jaws with teeth, and 

 the principal bones of the skeleton, reached a much larger size than 

 T. altidens, but was itself far surpassed in bulk by T. selwyni, whose 

 femur is nearly twice the size of that of Iguanodon mantelli of the 



^ " Ueber Stegoceras und Stereocephaluis " von Franz Baron Nopcsa, jun„ 

 Cenlralblatt fur Minéralogie, etc. No. 8, 1903. Stuttgart. 



