266 DE. AV. G. RIDEWOOD ON THE 



in the length of the postorbital portion o£ the head ; the latter 

 is the more probable supposition. The interopercular is a large, 

 flat lamina of bone ; it lies hidden by the lower part of the pre- 

 opercular and is not sculptured. 



The supratemporal differs considerably in shape and relative 

 size in the two skulls. In the smaller skull it is a small bone 

 which fits into the depression between the posterior ends of the 

 parietal and squamosal. Only a small portion of it is superficial 

 and sculptured, and the tubular portion that carries the sensory 

 canal is coutinued backward to about the same transverse level 

 as the tip of the epiotic prominence. In the larger specimen the 

 supratemporal is of fair size ; it projects downward and outward 

 from the parietal and squamosal so as nearly to reach the upper 

 edge of the opercular bone, and its anterior edge unites by a 

 serrated suture with the posterior edge of the upper of the large 

 postorbital plates. 



Gh'cumorhifal Series (fig. 15). — The nasal bones have already 

 been mentioned in dealing with the cranium. The orbital ring- 

 is complete and consists of five bones. The preorbital forms the 

 anterior half of the upper border of the orbit, and the uppermost 

 of the postorbitals the posterior half; the other two postorbitals 

 are very large cheek-plates ; there is one suborbital. These bones 

 are all sculptured except in certain elliptical areas, within each 

 of which is an opening for the sensory canal. 



Maxillary Series (fig. 15). — The gape is bounded above by 

 both premaxilla and maxilla, the former bearing 16 or 18 teeth 

 and the latter from 30 to 35 teeth, arranged in a single row. The 

 teeth are uniform in size, and are rather cylindrical in shape, 

 somewhat laterally compressed, with very slight curvature and 

 with bluntly conical tips. The posterior part of the premaxilla 

 is overlapped by the nasal in such a manner as to suggest that 

 there is no freedom of movement between these bones. The 

 edentulous portion of the maxilla that lies along the postero- 

 ventral surface of the premaxilla is long and tapering, and extends 

 as far as the median plane of the head. The extremities of the 

 tW'O maxillae thus meet one another behind the premaxillary 

 symphysis, but they do not themselves unite in any definite 

 manner. The exposed part of the premaxilla is sculptured, but 

 the maxilla exhibits no sculpturing, or just a little near the roots 

 of the teeth. There is no surmaxilla. 



Mandibular Sei^ies (figs. 15 and 16). — The coronoid process 



