16 FISHES OF ILLINOIS 



and caudal region of a form (Crossopholis magnicaudatus) discovered 

 in the Eocene Green River shales of Wyoming by Cope. 



The fishes of this family, in addition to their growing economic 

 importance in America, are of exceptional interest to biologists 

 on account of their primitive shark-like* form and characters, and 

 their consequent importance in tracing the descent of the bony fishes. 



Genus POLYODON Lacepede 

 (paddle-fishes) 



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

 and widening forwards; caudal fulcra j 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 cat) 



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



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

 69 (folium); F. F„ I. 2, 82 (folium), II. 7, 464, II. 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 4 J in 

 length without snout; caudal peduncle slender, tapered, nearly cylindric- 

 al 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 l.S 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) 

 S.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 S\ in interorbital space, situated nearly over tip of 

 mandible and directed obliquely downward and sidewise; mouth very 

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

 opening; 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 aim st or quite to the ventral fins in adults; gill- 



* The American paddle fish (Pnlyadon 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." 



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



