122 



CRETACEOUS AND TERTIARY FISH. 



row dental area on external oral extremity of beak, and another 

 still shorter along inner edge. A fifth area, small, varying in 

 elliptical pattern, at posterior symphyseal bevel opposite front of 

 largest oral dental area, and followed by a prominent ridge which 

 is convex with about two rather prominent longitudinal ridges, 

 and curving back forms edge of mandible ramus posteriorly 

 inside. 



Upper maxillaries a little more than twice as long as wide, and 

 their depth a little less. Form generally depressed. Upper sur- 

 face of each with a deep wide gutter extending forward about two- 

 thirds its length and ending in a deep pit, anterior to which area is 



Fig. 71. — Edaphodon mirificits Leidy. (Type of Ischyodus gaskillii Cope, 

 from Hussakof.) 



flat and horizontal. Sides of upper maxillaries flat and sloping 

 obliquely out. Lower surface with prominence in front sloping 

 forward, its crest giving rise to an elongated round dental area 

 sloping slightly down behind, where a crest forms, which gives 

 rise in turn to largest dental area. Latter extends well back and 

 close to inner edge, rounded, and also sloping down concavely 

 behind, while laterally it also extends well towards outer edge. 

 Just external to largest dental area another elongated dental area 

 arising on a slight convexity opposite hind region of anterior 

 dental areas, and extending back opposite deep posterior con- 



