MONOCLONIUS CANADENSIS. 



95 



grooves in outer wall of dental chamber deeply impressed toward their upper ends by a second series of groove terminations, 

 an evidence of two roots in the teeth belonging to this jaw, such as are characteristic of some of the species of the Ceratopsidre 

 (Agatkaumida?). Height of dental chamber much reduced forward. A number of large foramina present in the outer sur- 

 face. Front border, as viewed from the side, sinuous, rugose, for its union with the predentary bone. Twenty-three alveolar 

 grooves are present in the dental chamber (imperfect posteriorly) of the specimen figured. A small symphyseal surface is 

 present in the front lower border. 



Measurements of ramus of lower jaw. 



Mm. 



Extreme length at mid-height _ 0. 398 



Depth at mid-length _ 116 



Distance from upper border, a little in advance of front end of dental chamber to lower posterior border 



of symphyseal surface _ 137 



Height of facet for articulation of predentary bone 096 



Distance from top of coronoid process to lower border IUj 



Breadth of coronoid process from point of anterior hook backward 097 



Thickness at center of upper coronoidal expansion 024 



Thickness of coronoid process at its mid-height . 038 



Antero-posterior diameter of symphyseal surface . 055 



Height of same _ . 025 



Width of larger alveolar grooves at middle of dental chamber 009 



Six grooves in a space of '_ 072 



Height of grooves from their base to upper edge of outer alveolar wall, at middle of dental chamber. . 028 

 Height of same anteriorly _ 044 



A maxillary bone (not figured) with teeth that are double fanged is referred to this species. One of the teeth is shown 

 on PI. XVIII [XIX], figs. 3 and 4. 



A separate tooth, presumably from the. lower jaw, is also figured on PI. XVIII [XIX]. It was found separately, but on 

 account of its having two roots, agreeing thus with the evidence of the alveolar grooves of the mandibular ramus just described, 

 it is likewise referred to M. canadensis. 



The discovery of this specimen is of the greatest importance, since it affords the first defi- 

 nite information regarding the character of the parietals and squamosals that are associated 

 with the type of frontal horn cores shown in 

 Marsh's type of Ceratops montanus. A com- 

 parison of the frontal horn of the type of the 

 present species with that of Marsh's type of 

 C. montanus makes it apparent that they are 

 essentially the same, and I do not hesitate to 

 remove the present species from the genus 

 Monoclonius Cope and place it in that of 

 Ceratops Marsh. Whether or not it should be 

 regarded as specifically distinct from O. mon- 

 tanus I am unable to say without further 

 study, and this question will be left for that 

 portion of the present volume devoted to a 

 revision of the genera and species. It is 

 true that Professor Marsh had referred. the 

 broad squamosal shown in PL III, fig. 1, to 

 Ceratops montanus, but since that specimen 

 was found at a place about 15 miles distant 

 from the locality that yielded the type, 



Marsh's correlation, though possibly correct, is purely conjectural, and to Lambe's fortunate 

 discovery we are indebted for positive knowledge concerning the actual association of these 

 important elements of the skull in this type of the Ceratopsia. 



The squamosal (No. 1254a, Geol. Surv. Canada) found associated with the type of the 

 present species exceeds in length that of any squamosal yet found from the Judith River beds. 

 The portion posterior to the quadrate groove is more than twice the length of the anterior por- 

 tion. Posteriorly it is much contracted and elongated and is already clearly assuming the 

 form shown by the squamosals in the later genus Torosaurus, from the Laramie. The quad- 



Fig. 97. — Anterior dorsal vertebra of Monoclonius canadensis. One- 

 fourth natural size. A, Front view; B, left side view, a, Anterior 

 face of centrum; d, diapophysis; ft, facet for head of rib; n, neural 

 canal; s, neural spine; I, facet for tubercle of rib; 2, prezygapophy- 

 sis. z' . postzygapophysis. After Lambe. 



