LAMPKEYS AND FISHES OF INDIANA. 149 



Eyes present in the adults, rudimentary in the young. Nasal organs 

 in front opening just in front of the eyes, behind ending iu a blind sac. 

 Egas small. 



The lampreys probably do not burrow into the bodies of their prey as 

 do the hag-fishes, but content themselves with tearing away bits of flesh 

 from the surface. They are often taken while adhering to the bodies of 

 the larger fishes. On the other hand, the fishes sometimes retaliate by 

 swallowing the lampreys. The lampreys likewise employ the sucking 

 disk to fasten themselves to stones and other bodies, thus obtaining rest- 

 ing places. While thus attached, the water for respiration must pass 

 both in and out through the gill openings. Some of the larger lam- 

 preys, especially the Sea Lamprey, are used as food. It is not highly 

 regarded, iu this country at least, and is said to be difficult to digest. 

 In England a fresh-water species is largely employed as bait in the cod 

 fisheries. For interestiug information on lampreys see 12, 1884, 677. 



The lampreys undergo a marked change during their growth. For a 

 time, until they reach a considerable size, they are worm-like, blind and 

 toothless. 



GENERA OF PETR03IYZ0NTID.E 



A. Sucker relatively small and with few teeth ; mouth overhung 

 with a crescent-shaped horny plate, which terminates at each 

 end in a distinct tooth ; tongue armed in front with a crescentic, 

 serrated, horny plate. Ammoccetes, p. 149. 



AA. Sucker large in adults, and furnished with numerous teeth, which 

 are in rows radiating from the mouth; horny plate above the 

 mouth short and with but two or three teeth, which are placed 

 close to one another. Petromyzon, p. 150. 



Genus AMMOC(ETE.S Dumeril. 



Small freshwater lampreys. Suctorial disk relatively small and fur- 

 nished with few teeth. Horny plate over the mouth elongated and 

 terminating at each end in a distinct tooth. Anterior border of the 

 tongue furnished with a crescent- shaped horny tooth, which is dentated, 

 the middle denticle being largest. Dorsal fin continuous, but with a 

 broad shallow notch. 



A single species only is found with us, and this is regarded as identical 

 with that found in Europe. 



