THE LOWER CHALK OF DOYEE. 443 



pyrites (fig. 1, pi) occupies the probable position, and has somewhat 

 the form, of the malleolus of a palatine ; and it is quite possible that 

 this bone is merely incrusted with pyrites. 



The irregular bone (fig. 1, no) lying between the preorbital process 

 of the frontal and the maxilla, from the position which it occupies, 

 seems to be either a somewhat displaced nasal bone, or a preorbital 

 mucous bone. 



Opercular Bones. — The large size of the opercular elements makes 

 them a prominent feature in this fossil. The prceoperculum has a 

 concave anterior border which embraces a considerable part of both 

 the hyomandibular and quadrate, and extends from the angle of the 

 mandible to within three fourths of an inch of the sphenotic. Its 

 lower and hinder borders, being thin, are somewhat broken ; but the 

 general form of the bone may be judged from fig. 1 (pr.op). 



The operculum (op) is a large quadrilateral bone, articulating with 

 the hyomandibular by a thickened portion, which is situated near its 

 upper and anterior corner, and from which lines are seen to radiate 

 over the slightly convex external surface. Above the articulation 

 the bone inclines a little inwards and forms a process, which nearly 

 reaches the angle of the pterotic. Below the articulation the anterior 

 border is hidden by the overlapping praeoperculum. The hinder free 

 border is nearly semicircular. The lower margin is partly over- 

 lapped by the piece of the suboperculum which is preserved (s.op). 

 The latter bone occupies, as nearly as possible, its normal position. 



If this specimen possessed an interoperculum, it has been lost on 

 the left side. On the underside of the specimen, however, there is 

 a bone which is probably the right prseoperculum ; and directly below 

 this there is a broken bone which occupies the position of an inter- 

 operculum. 



Posttemporal. — Immediately above and behind the operculum there 

 is a large flat bone (pt.tem), which appears to be an expanded post- 

 temporal, occupying, as it does, so nearly the natural position of that 

 bone, and having at its interior portion two processes, such as a 

 posttemporal would be likely to have, for articulation with the skull. 

 It may perhaps be asked if this is not a portion of the operculum of 

 the right side, which has been displaced ; but a close examination 

 shows, I think, conclusively, that such is not the case. The edges of 

 this bone are broken ; and therefore its precise form is uncertain. 

 Its thickest part is just behind the oblique depression seen in the 

 figure towards its anterior end. The lower edge in this region is 

 produced into a process ; and the upper anterior corner seems to have 

 been elongated in a somewhat similar manner. The hinder part is 

 thin ; and the outer surface is convex and marked by lines radiating 

 from the thick end of the bone, as shown in the figure. 



Skull. — The form and structure of much of the skull can be made 

 out ; for the upper surface and left side are almost perfect. The 

 surfaces of the bones are much denuded ; but this in some instances 

 affords a clue to their extent. The anterior part of the skull, in- 

 cluding the whole extent of the frontals, is comparatively flat, there 



