Monoclonius canadensis Lambe 1902

Monoclonius canadensis. Sp. nov.

Plate XVII, figs. 3 and 4, and plate XVIII, figs. 1 - 7.

This species is founded on a squamosal, part of a parietal, a jugal, a supraorbital horn core, the left ranlus of the lower jaw, and an anterior dorsal vertebra, With some other parts of the Skull, not yet fully determined, of one individual. A right ramus of another individual is shown on plate XVIII, and a separate horn core on plate XVII.

A right mandibular rarnus, referred to this species on account of its resemblance in form to the one shown above, is described farther on.

The horn core (fig. 18, page 64) rises above the orbit from the postfrontal of Which it forms a part. The postfrontal unites behind, by suture, With the squarnosal and below with the jugal. The orbit is oval with the longer diameter vertical, its upper curve lying close under the base of the horn core, its margins not ridged. The horn core is small, about 216 cent. long from the upper edge of the orbit to its summit and 228 cent. in circumference near the base, circular in section and solid. Squamosal somewhat triangular in shape, fiat, moderately thin, its outer edge smooth, rounded, wavy in outline so as to produce six minor convex curves, shorter and more pronounced near the front. Its outer front edge is deeply emarginated, with a shallower concavity limiting the outer termination of the jugal suture (see figure 18), inside of which is the suture for the union with the postfrontal. The inner border is slightly concave. The lower surface near and parallel to the inner posterior end is broadly and shallowly grooved for the reception of a long. slender bone, triangular in section, that projects backw-ard and inward, its outer edge continuing the curve of the sqnamosal. Ilrobably this slender bone represents the anterior end of:1 forwardly bent, side extension oi the parietal, such as occurs in the species lifonocloníus bel/í, in which case a fontanelle of moderate size might be expected on the inner side of the squamosal.

In figure IS the underlying bone (imperfect posteriorly) is indicated hyadotted outline under the sqnamosal beyond which it projects; its outer free edge shows a round cdged convexity in continuation of the sinuosities of the squamosal. The proximal inner margin of the squainosal is hciit at right angles to the plane in which the rem-ainder of the bone lies and its under surface is deeply excavated in its inner front part for some distance back from the posttrontal suture.

[table omitted]

[table omitted]

With the parts of the head, shown in fig. 18, Was also found an anterior dorsal vertebra (fig. 19), of rather small size. The faces of the Centrum of this vertebra are slightly concave. Next following is the description of a right mandibular ramus, found separately in 1897, but agreeing in size With the one depieted in fig. 18.

Ramus of lower jaw (right). Cat. Ne. 284. Ramus of lower jaw (plate XVIII, figs. 1 and 2) stout, With an inward bend at mid-length, low and thick behind, elevated and laterally compressed in front Where the inner surface is shallowly concave. Excavated posteriorly below for nearly one-third of its length, the excavation extending upwaild along the back Surface of the coronoid- processa and an' teriorly as the mandibular canal leading forward to the mandibular groove in th; "' m lower border. The dentary canal, between theouter alveolarwall and the outer surface, enters from the upper and anterior part of the excavation by a large opening. Coronoid process stout, upright, hooked forward and flattened laterally above, its outer, upper surface rugosely striated. A broad, low ridge, least defined toward the centre, runs at about mid-heigth, along the outer side, the surface, in a general way, above and below, retreating obliquely inward. The dental chamber, straight, starting at a low level behind, inclined strongly upward and slightly outward toward the front, its lower edge making' an angle of about 20 ° with the lower border. Alveolar 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 Ceralopsídóo (lgat /iazunidre). Height of dental chamber much reduced forward. A number of large foramina present in the outer surface. 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 symphyscal surface is present in the front, lower border.

[table omitted]

[table omitted]

A maxillar Y bone not c: figured with teeth that are double fanfrcd o, is referred to this species. One of the teeth 1 s shown on plate XVIII, figs. 3 and 4.

A se P arate tooth. P resumabl from the lower.aw, is also o figured on plate XVIII. It. was found se p aratel, but oii account of its havinfi' D two roots, D arrreeinn‘ D thus with the evidence of the alveolar grooves ot the mandibular rainus just described, it is likewise referred to M. canadensis.