Mr. R. Walker on Fossil Fishes of Dura Ben. 77 



anterior edges projecting forward a little beyond the commence- 

 ment of the parietals. The parietals (pa.) are rather large 

 bones, and, like the frontals, join each other on the middle of 

 the cranium by a suture of square edges ; their posterior ends 

 are truncated where they meet the supra-occipital, the anterior 

 somewhat regularly rounded, the round terminating on the 

 antero -lateral edges in points, which are rendered more apparent 

 by their lateral margins being concave. Into these concave mar- 

 gins the upper edge of one of two bones, which may represent 

 the squamosal (sq.), is attached; they meet the epiotic poste- 

 riorly, and fill in the spaces between the parietals and operculum. 

 The operculum (op.) and sub-operculum (s.op.) are distinct bones, 

 co-adapted, and look somewhat like a single rudely crescent- 

 shaped plate, with the concave edge turned upward, rounded 

 behind, and slightly so in front. The opercular and squamosal 

 bones are succeeded in front by two bones, the upper of which 

 may represent the supra-temporal (s.t.), and meets the lower 

 margin of the parietal ; the lower bone, which may be the hyo- 

 mandibular (h.m.?), fills in the space between the supra-temporal 

 and the maxilla. Both these bones have their exposed surfaces 

 ornamented by radiating strise ; on the upper bone the striae 

 proceed from a raised horizontal centre, on the lower bone from 

 a raised nearly vertical centre. The frontals (fr.) are about 

 half the length of the parietals, and not much more than half 

 their breadth; the posterior margins, by which they meet the 

 parietals, are concave, the anterior somewhat convex. There is 

 a small bone on each side of the head, probably the post-frontal 

 (pt.f.), which fits in between the frontals and the supra-temporals. 

 The next bone in front is perhaps the post-orbital (pt.o.), which 

 forms the posterior boundary of the orbit; its margins unite 

 with the frontal, post-frontal, and supra-temporal; the lower 

 edges unite behind the middle of the orbit with the sub-orbital 

 bone (sb.o.), which thus forms the lower boundary of the orbit 

 behind and fills in the space between the post-orbital and the 

 maxilla. The bones in front of the orbits are not distinctly 

 defineable on any specimen that I have seen ; but it appears as if 

 the lower edge of the pre-frontal passed back between the orbit 

 and the maxilla till it met the sub-orbital. Neither are the 

 bones before the frontals clearly legible ; the space seems to be 

 occupied by a number of small four- and five-sided plates, which 

 may represent the ethmoid, &c. The maxillae (mx.) do not 

 appear to have been very strong ; externally they were orna- 

 mented like the bones of the head, and had a row of small (as 

 far as I have seen) equal-sized teeth on their lower edges. There 

 appears to me to be a pretty distinct pre-maxilla (p.mx.), which 

 joins the maxilla under the anterior margin of the orbit, and 



