148 CRETACEOUS AND TERTIARY FISH. 



tooth deeply excavated, leaving trenchant edges all around and 

 longer ones slightly more approximated than edges of upper 

 surface. Length about 29 mm. 



This was probably inclined from left downward to right end, 

 and beginning at former greater portion beveled as triturating 



Fig. 91. — Pycnodus robustus Leidy. (Type). 



surface, leaving lower right portion more convex. Coloration 

 brownish and all about edges rather pale slaty. 



Formation and locality. Only the type, described above, with- 

 out definite locality or geological horizon (G. H. Cook) is known. 

 It is now in the collection of the Academy. 



Order LEPIDOSTEI. 



THE BONY GANOIDS. 



Skeleton bony. Subopercle and preopercle present, also coro- 

 noid and mesocoracoid. Branchiostegals present. Ventral fins 

 abdominal, with basilar segments rudimentary, as in ordinary 

 fishes. Primary radii of hind limb generally reduced to one rudi- 

 ment. Optic nerves form chiasma. Intestine with spiral valve. 

 Arterial bulb with several pairs of valves. Air vessel lung-like, 

 cellular, connected, with oesophagus by duct. Skin covered with 

 ganoid or cvcloid scales. Tail heterocercal. 



