STEGOCERAS. 



97 



Fig. 98. — Posterior crest of Monoclonius belli, from 

 Red Deer River. One-eighteenth natural size. 

 The dotted lines are from a drawing of the head 

 of Torosaurus gladius Marsh, as seen from above. 

 P, Parietal; S, squamosal; F, fontanelle. After 

 Lambe. 



His original description is as follows: 



The bone, figured on the above plate [PI. XXI], 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. gladius of 

 Marsh from the Laramie of Wyoming. 



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 ' j '; / \ ■ ; 



of the bone has been applied to the figure, slightly modified, of the skull ; \ / \_ / ;' 



of T. gladius, as given by Marsh in the Sixteenth Annual Report of the \ y' } j 



United States Geological Survey. (/'• % 



The parietal element from Red Deer River is symmetrical, T-shaped, j i 



with a subcylindrical shaft expanding rapidby both in front and behind. / .£'-'' ' : '.\ 



Anteriorfy the expansion is concave below, strengthened above by a median, 

 rounded ridge in continuation of the central shaft, and thinning out later- 

 ally. 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 one-third the. size 

 of that of T. gladius, 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. 



Mm. 



Extreme length of specimen (imperfect anteriorly) along median line 0. 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 _ : 180 



Breadth of same at mid-length _ '■_ . 065 



Thickness of same at mid-length 053 



Thickness of anterior expansion at center 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 of shaft. .... l . 035 



Antero-posterior diameter of fontanelles 416 



Belly River series, Red Deer River, 189S. 



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



After a careful study of the type of the present species, together with that of M. canadensis 

 Lambe, one can not avoid being convinced as to their generic identity with Ceratops montanus 

 Marsh, while at the same time the great dissimilarity shown in the parietals and squamosals of 

 these species when compared with the same elements in Monoclonius dawsoni Lambe affords 

 evidence additional to that already pointed out as obtaining in the frontal horn cores, in favor 

 of the generic distinction of the three former species from that of the last-mentioned species. 



STEGOCERAS Lambe. 1902. 



Type species, S. validus. 



Original description in Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 68 and 69: 

 Nopcsa, F. Baron, Centralblatt fur Mineralogie, 1903, p. 266. 

 Osborn, H. F., Contr. Canadian Pal., vol. 3 (quarto), pt. 3, 1902, p. 21. 



This genus was founded by Lambe on some problematical reptilian remains from the 

 Judith River beds of Canada. Although they are probably not referable to the Ceratopsidas 

 they will be considered here for the reason that Lambe referred them to that family. 



MON XLIX — 07 7 



