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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



ness of the interorbital bridge and bony rostrum would perhaps be a source of weakness if 

 these very long frontals were not coalesced in the mid-line. The rostrum is also braced on 

 the ventral side by the parasphenoid, which in turn is fastened posteriorly by strong 



epiot soc 

 GONORHYNCHUS 



. Fig. 65. Gonorhynchus greyi. Top view. After Ridewood. 



ascending processes to the low cranial vault. The down-bending of the rostrum and the 

 vaulting of the roof of the oral chamber have probably conditioned the marked shortening 

 of the prefrontal (parethmoid) in the vertical plane. The anterior preorbital (lacrymal) 

 is also involved in this prolongation and so are the slender nasals, but to a far less extent, 

 while the mesethmoid is represented on the dorsal surface only by a small terminal bone. 

 As in the sturgeon, the rostrum is curved downward so as to project in front of the 

 very small mouth, while the palatopterygoid arch is curved upward and then downward 

 and forward to form the roof of a special cavity for the small mouth parts (Fig. 66). The 

 premaxillse are small rods only about half the length of the rod-like maxillae. They lie 

 below and in front of the maxillae. The mandible is relatively stout and much longer than 

 the maxilla, but only the front part of the mandible enters into the gape, owing to the fact 

 that the ascending ramus of the dentary is tilted upward at a sharp angle to the anterior 

 process of the articular. In other words, "The lower margin of the gape is nearly at right 

 angles to the long axis of the mandibular ramus" (Ridewood, \9QSb, p. 365). From the 

 relative robusticity of the mandible and the presence of strong ridges on the hyomandibular 

 and preopercular it may be inferred that the adductor mandibulae muscles are fairly 



