146 CRETACEOUS AND TERTIARY FISH. 



and united by peg-and-socket articulation in connection there- 

 with. Fin-rays robust, majority well-spaced and articulated, 

 fulcra absent, except perhaps quite at base of caudal fin. Dorsal 

 and anal more or less extended. 



This family, of which all its members are extinct, is appar- 

 ently most closely related to the sturgeons, near which it has been 

 placed. About 15 genera have been described. 



Genus PYCNODUS Agassiz. 



Pycnodus Agassiz, Poiss. Foss., II, 1835, p. 183. Type Zeus platessus Blain- 

 ville, first species, restricted by Woodward, Cat. Foss. Fishes, III, 1895, 

 p. 276. 



Periodus Agassiz, 1. c, p. 201. Type Periodus hoemigii Agassiz, monotypic. 



Trunk deeply fusiform, gradually passing into slender caudal 

 peduncle. Teeth smooth or with slight apical pit and feeble 

 rugosity. Oral vomerine surface slightly convex from side to 

 side, with five longitudinal series of teeth. Splenial dentition com- 

 prising three series of teeth, innermost largest. Head and oper- 

 cular bones externally rugose and punctate. Neural and hcemal 

 arches of axial skeleton of trunk expanding to encircle notochord. 

 Scales covering front part of body before median fins. Fin rays 

 delicate, spaced, articulated, somewhat divided distally. Pelvic 

 fins present. Dorsal and anal low, fringe-like, former occupies 

 greater part of back and latter much shorter, arising posteriorly. 

 Caudal with slightly excavated hinder border. 



About 32 species have been described. 



Pycnodus phaseolus Hay. 



Pycnodus phaseolus Hay, Amer. Nat., XXXIII, 1899, P- 788 (name only, 



based on L,eidy). 

 Pycnodus faba (nee Meyer) Leidy, Rep. U. S. Geol. Surv., I, 1873, pp. 292, 



349, PI. 19, fig. 15-16. Greensand Marl of Crosswicks, Burlington 



Co., N. J. 

 Cope, Rep. U. S. Geol. Surv. Terr.. II, 1875, p. 280. (Greensand No. 



? of N J.) 



Jaw fragment with three broad teeth arranged obliquely parallel 

 with one another from within backward and outward. Outline 



