Monoclonius bellil, 1902

Lambe L. M., 1902, New genera and species from the Belly River Series (mid-Cretaceous), Geological Survey of Canada Contributions to Canadian Palaeontology 3, pp. 25-81 : 66-67

Monoclonius bellil . Sp. nov.

Plate XX, figs. 1 and 2 .

The bone, figured oii the above plate, is interpreted as representing the coalesced parietals of the posterior crest of an undescribed species of Monoclonius, probably ancestral to such later forms as Torosaurus latus and T D frladius of Marsh, from the Laramie, of \Vyo- min g. To facilitate an understanding of the view held as to the position the parietals probably occupied relative to other bones of the head, a drawing of the bone, has been applied to the figure, slightly ino- - dified, ot n the skull of T. gladius, as. given by Marsh, in the Sixteenth Annual Report ofthe United States Geological Survey.

The parietal element from Red Deer river is symmetrical, T-shaped, wlh a sub- cylindrical shaft expanding rapidly both in front and behind. Anteriorly the expansion is concave below, strengthened above by a median, rounded ridge in continuation of the central shaft, and thinning out laterally. Posteriorly the shaft divides, nearly at right angles to itself, to either side. so as to form a strong transverse bar slightly concave at mid-length above and convex below, thin at its front edge and thickest behind. The posterior border is angularly rounded.

The space on either side of the shaft represents the inner halves of the supratemporal fontanelles. The bone missing from the specimen would complete the outer border of the fontanelles and effect a union With the inner margins of the squamosals- The lower face of the anterior expansion, on either side of the median line, is striated by distinct furrows that follow down the lower lateral sides of the shaft, as deep grooves, and curve outward on to the transverse bar. The anterior upper surface also exhibits similar grooves that do not, however, pass beyond the mid-length of the shaft.

The parietal, imperfect at its anterior end, is about 011e-third the size of that of T. gladíus and would probably represent a proportionately smaller animal, an earlier and more generalized form of the genus with larger fontanelles than its later Laramie successors.

Measurements of parietal bone.
	N I
Extreme length of speciınen (imperfect anteriorly) along median line.	584
Breadth of front expansion from median line to left edge of specimen	' 173
Breadth of posterior border from median line to left edge of specimen.	' 305
Circumference of shaft at mid-length.	ISO
Breadth of same at mid-length.	' 065
Thickness of same at mid-length.	' 053
Thickness of anterior expansion at centre on median line	' 041
Thickness at anterior end of specimen on median line	' 018
Thickness on median line midway between posterior border and narrowest part ef shaft.	' 035
Antero-posterior diameter of fontanelles	' 416

Belly River series, Red Deer river, 1898.

This species is dedicated to Dr. Robert Bell, the administrative head of the Geological Survey.

Figures

PLATE XX. Fig. 1. Monoclonius belli, Lambe, parietal element of posterior crest, superior view; one-third the natural size. Page 66. Fig. 2. The same, inferior view. Fig. 3. Monoclonius dawsoni, Lambe, rostrai bone, side view; one-half the natural size. (Provisionaily associated with M. dawsoni). Page 63. Fig. 4. Outline of section of at “. ” same c Fig. 5. Horn core with an asymmetrical base. Kot specifically determined. Fig. G. Sectional outlines of same at a and h” g, groove for premaxilla