37 
larger than in A. omatus. This is only natural, for in forms where the 
brow horns are large the frontal fontanelle is usually nearly or completely 
closed. 
The supratemporal fossae do not appear to differ materially from those 
of A , omatus. They open posteriorly, as in that species and in the genera 
Torosaurus and Triceratops. 
The crest is large, rectangular, and quite flat (Plate XXII). The 
fontanelles are proportionately much longer than in A. omatus and, as in 
that species, are wholly within the parietals. The crest is relatively thin, 
especially in advance of the fontanelles. The maximum thickness of the 
crest, through the posterior portions of the squamosals and parietals, is 
30 mm., but the average thickness is not more than half this. 
The squamosals are long and narrow, as in A . omatus. The epoccipitals 
are so thoroughly fused with the squamosals that they appear as serrated 
edges rather than separate ossifications. The same is true of the large 
epoccipitals on the posterior edge of the parietals. The squamosals are 
marked by vascular grooves both above and below. 
The parietals resemble those of A. omatus, but are thinner, and the 
epoccipitals are much thinner and smaller. As in A. omatus, there is a 
pair of short, thick, hook-like processes, thoroughly fused to the median 
posterior extremity of the superior surface of the parietals. On the superior 
surface of the parietal, in advance of the fontanelle, there is an area in 
which the surface is lowe than the rest of the bone and quite smooth. 
This is a backward extension of the floor of the supratemporal fossa and 
the bone is very thin. Except for these areas in advance of the fontanelles 
the parietals are covered with vascular markings. 
Measurements of Type 
Mm. 
Length, tip of rostral to extremity of crest 1,660 
Greatest breadth of skull (anterior portion of crest), as restored. 730 
Breadth of posterior portion of crest, including epoccipitals 660 
Tip of rostral to anterior edge of nasal horn core, between vertical points. 290 
Anterior edge of nasal horn core to anterior edge of frontal fontanelle 425 
Height of nasal horn core 72 
Posterior tip of rostral to anterior edge of nasal horn core 155 
Length from tip of rostral to anterior border of orbit 600 
Length, anterior border of orbit to extremity of crest 1,060 
Greatest depth of nose in front of nasal horn core 220 
Greatest breadth of upper beak (premaxilles) about 160 
Distance between antero-external edges of orbital rims 260 
Distance between brow horn cores at base 110 
Distance between brow horn cores at tips 310 
Length of brow horn from superior border of orbit 310 
Circumference of brow horn near base 255 
Height of tip of horn core above lowest part of superior border of nasals. , 245 
Greatest diameter of orbit 110 
Greatest diameter (fore and aft) of parietal fontanelles 280 
Transverse diameter of parietal fontanelles 150 
Tip of rostral to occipital condyle. 800 
Occipital condyle to extremity of crest 860 
