120 The Ottawa Naturalist [January 



slightly depressed area exterior to which the lateral angulation curves 

 slightly downward. Anteriorly the thickness of the bone is suddenly 

 increased on the lower surface a short distance back from the front 

 edge. This edge is conspicuously notched by about from ten to twelve 

 grooves which pass inferiorly backward across the thinned marginal 

 area. 



The nasal bones are contiguous along the midline of the cranium 

 throughout their length, except possibly at their extreme anterior end. 

 They are broad for the most part and curve downward outwardly to 

 meet the premaxilla and the prefrontal. They arch over the nasal 

 passages and their openings which latter are placed far forward. In 

 advance of the openings the nasals continue narrowly forward for a 

 short distance over the premaxillae on either side of the midline, but 

 the exact outline of their anterior ending is obscured. Posteriorly they 

 appear to bifurcate, the exterior branch overlapping the frontal while 

 the interior one continues, much attenuated, on the inner side of the 

 frontal to the summit of the dome-shaped superior surface. This 

 surface bifurcation of the nasal is not a division in reality, as the bone 

 underlies the narrow front termination of the frontal. 



A notable feature in the skull of Cheneosaurus is the presence of 

 a large supraorbital bone which enters into the formation of the orbital 

 rim almost to the same extent as the postfrontal. This bone is roughly 

 subtriangular in shape and is in contact posteriorly with the post- 

 frontal and frontal, superiorly with the frontal, and anteriorly with 

 the prefrontal. Its lower edge for the most part forms the antero- 

 superior portion of the curve of the orbital rim. Infero-anteriorly it 

 extends narrowly downward and overlaps the upper end of the 

 lachrymal. 



The postfrontal has a somewhat larger surface area than the 

 supraorbital and meets it anteriorly in a zigzagged suture. ' Posteriorly 

 it overlaps the squamosal extensively. Superiorly its posterior half- 

 length bounds the supratemporal fossa externally at the front, while 

 the remainder of its upper half-length joins the frontal in a jagged 

 suture. 



The frontal is larger than the prefrontal, and is of an irregular 

 shape. It is in sutural contact with the nasal, the prefrontal, the 

 supraorbital, the postfrontal and the parietal. For nearly the whole 

 of its anterior half-length it is separated from its fellow along the mid- 

 line by the narrow backward extension of the nasals. It forms the 

 greater part of the dome-shaped elevation of the cranium rising from 

 behind, and descending on the anterior slope its forwardly directed 

 attenuation overlaps the nasal. For a short distance forward from its 

 junction with the parietal, equal to about one-fifth of its total length, 

 its surface is lower than the part that rises into the dome-shaped 

 prominence and is defined from it by an overhanging transverse fold 



