34 PROCEEDINGS OF THE 



the supposed maxilla, and its oral border is produced to a point 

 whicli works a<;aiiist the outer face of the beak of the opposing 

 bone of the mandible (lig. 4 E). Tlie mandibular bone is evidently 

 only one element of an otherwise persistently cartilaginous jaw*, 

 its hinder half must liave been sheathed at least on the outer face, 

 but its anterior half would be exposed on the outer face of the 

 jaw. Its oral border, opposed 1o the sui)posed maxilla, is a sharj), 

 straight cutting edge, of which the outer surface would work 

 against the inner surface of the upper bone. This cutting edge 

 terminates forwards at a notch separating it from a beak-like 



Crushed edge of head-shield and jaws of riglit side, inner view, of Dinichthij/; 

 intermedins, from the Upper J)evonian of Ohio, U.S.A. c. crushing edge 

 of pterygoid arcade ; d. dentary ; ecf. artieidation for preniaxiUa on lateral 

 ethmoid ; m-v. maxilla ; pmx. premaxilla; pr. articular proces.'^es of maxilla 

 and preniaxilla ; y)<. pterygoid arcade ; so. suborbital cheek-plate ; .r. down- 

 ward process from wall of cranium. (Brit. Mus. no. P. 9340.) 



anterior end, of which the postero-external face would work 

 against the antero-internal face of the opposing upper bone. 

 There is no facette for a symi)hysial union of the mandibular bone 

 with its fellow of the opposite side; and there seems to be no 

 doubt that a cartilaginous sympliysial region was interposed 

 between the two, because the opposing sufiposed premaxilla?, which 

 fix their position, are well separated in tiie middle line by the 

 rostral plate covering the mesethmoid. It has been suggested that 



* In an ailiedgenu8,Z)iMO»i^/os^o»jcr,thecartiIageof the mandible issufticiently 

 calcified to be preserved (C. R. Eastman, Bull. Mus. Comp. Zool. Harvard, 

 vol. 1. iyO(), pp. 25, 26, pis. iv., v.). 



