Native Fishes of Iowa. 163 



ceding. It attacks soft rayed fishes more often than the spiny 

 rayed fishes. Occasionally it is taken attached to Lefidos- 

 tetis. The dentition is variable. The maxillary tooth has 

 from two to three cusps, and the mandibulary from 6 to 12 

 cusps. In some specimens some of the discal teeth are 

 bicuspid, in others all the discal teeth are simple. 



I'his species attains a length of 10 inches, and is of no 

 economic importance. It ranges from Lake Erie to the Miss- 

 issippi valley, Minnesota, Kansas and Louisiana. 



The Lampreys are not really fishes, but they are usually 

 classified with them. Their affinities are perhaps as much 

 with the Batrachia as with the fishes. They undergo a meta- 

 morphosis as do the Batrachia. In the larval state they 

 are white, worm-like, toothless, and with rudimentary eyes. 

 During the larval state they live buried in the sand on the 

 banks of the stream just below the water's edge. 



A A Skull well developed, nostrils paired, mouth not sub-circular and 

 with true jaws. (The true fishes.) 



TJ Tail evidentl}- heterocercal. (The backbone running up into the 



upper lobe of the tail.) 



r^ Body almost entirely naked. Snout prolonged into a long flat blade 



which overhangs the broad terminal mouth. No barbels. 



Family 2. POLYODONTIDiE.— The Paddle-fishes. 



Spiracles present. Air bladder cellular and lung-like. One branchiostegal 

 ray. Opercle rudimentary, its skin produced in a long flap. Dorsal rays 55. 

 Anal rays 57. 



Genus j. Polyodon. — Lace^ede. 



3. Polyodon spathula. — Walbaum. — Spoon-bill. Paddle- 

 fish. 



This remarkable fish inhabits the Mississippi valley only. 

 It attains a length of 6 feet, is found more frequently in the 

 fall and then in bayous. It is not highly valued as a food fish. 



C^C^ Body with 5 series of bony shields. Mouth inferior, toothless, and 

 preceded by four barbels. Air bladder large and not cellular. 



