16 FISHES OF ILLINOIS 



(Crossopholis magnicaudatus) discovered in the Eocene Green 

 Rivers shales of Wyoming by Cope. 



The fishes of this family, in addition to their growing eco- 

 nomic importance in America, are of exceptional interest to biol- 

 ogists on account of their primitive shark-Hke* form and char- 

 acters, and their consequent importance in tracing the descent 

 of the bon}^ fishes. 



Genus POLYDON Lacepede 



paddle-fishes 



Gill-rakersf exceedingly fine, slender, and numerous; paddle broad 

 and widening forwards; caudal fulcraj of moderate size, 13 to 20 in num- 

 ber. Represented by a single species, confined to the rivers of the Missis- 

 sippi Valley in North America. 



POLYODON SPATHULA (Walbaum) 

 paddle-fish; spoonbill oat 



Walbaum, 1792, Artedi Pise, 522 (Squalus). 



G., Vlll, 346 (folium); J. & G., 83; M. V., 33; J. & E., I, 101; N., 51 (folium); J., 

 69 (folium); F. F., I. 2, 82 (folium), IL 7, 464, IL 8, 514, ff; F., 85; L., 7. 



Body fusiform, little compressed; large fishes with a smooth skin and 

 an elongate paddle-shaped snout; length 5 to 6 feet; depth 4 to 41^2 in length 

 without snout; caudal peduncle slender , tapered, nearly cylindrical in cross- 

 section, its least depth less than }/^ depth of body. Color pale to dusky 

 bluish olive; channel specimens (from Mississippi River) regularly lighter 

 in color than those from sloughs. Head large, its total length including 

 spathula and opercular flap 1.5 to 1.7 in length of head and body; eye to 

 back gill-opening about 3 in distance from eye to base of caudal; spathula 

 (from eye) 3.2 to 3.5 in length in adults, 2.3 to 2.8 in younger specimens 

 (1 to 2}/^ feet) ; greatest breadth of spathula (near tip) 3.4 to 4.3 in its length, 

 least breadth (near base) 5.3 to 5.4; a pair of minute barbels on under side of 

 rostrum, at a distance in front of mouth about equal to width of rostrum 

 at its base; eye small, about b]/2 in interorbital space, situated nearly over 

 tip of mandible and directed obliquely downward and side wise; mouth very 

 large, shark-like, its cleft equal to % distance from eye to back of gill-open- 

 ing; jaws and palate with numerous fine teeth in young specimens; lower 

 lip of spiracle with a small barbel-like lappet; opercular flap greatly elongate 

 and tapering, reaching nearly to front of dorsal fin in half-grown specimens 

 and almost or quite to the ventral fins in adults; gill-membranes connected, 



* The American paddle-fish {Polyodon spathula) was originally described by Walbaum 

 (1792) as a species of shark: and Rafinesque, who described the species under at least three 

 different names, was misled once into an elaborate description of it under the name Proceros 

 "a singular new genus of sharks." 



f These characters separate Polyodon from Psephurus, the paddle-fish of China. 



