FISHES 29 



Suborder i. Selachostomi. — Skin naked: i family. 



Family Polyodontidae. — The paddle-fishes. Body without scales 

 and smooth; snout spatulate and very long; teeth minute, present 

 only in the young; opercles rudimentary, prolonged behind on each 

 side to form a long flap; spiracles present; i branchiostegal ray; air 

 bladder cellular: 2 species and genera, i in China {Psephurus gladiiis). 



PolyodonLacepede. Gill-rakers very fine and numerous: i species. 



P. spathiila (Walbaum). Spoonbill; paddle-fish. Extreme length 

 1,800 mm.; extreme weight 150 lbs.; color olivaceous; head, with 

 opercle, more than half the length of the body; spatula one-third the 

 total length: Mississippi Valley; French Broad, North Carolina; Lake 

 Erie; often common in the larger streams and lakes, where it feeds on 

 small organisms in the mud; used for food and the roe made into caviar. 



Suborder 2. Glaniostomi. — Skin with bony scales; sturgeons: 

 I family. 



Family Acipenseridae. — Sturgeons. Large fish with 5 longi- 

 tudinal rows of keeled bony plates on the body, a middorsal series and a 

 lateral and an abdominal series on each side, between which are small 

 plates or granules; mouth ventral and toothless, in front of which pro- 

 jects a long snout ; 4 barbels in a transverse row in front of the mouth ; 

 gill-slits 4, with an accessory opercular gill; no branchiostegal rays; 

 ventral fins posterior; median fins with spine-like projections called 

 fulcra: about 20 species; 7 species and 3 genera in America. 



Key to the Genera of Acipenseridae 



ai Spiracles present i. Acipenser. 



3.2 Spiracles absent. 



bi Belly covered with subrhombic plates 2. Scaphirhynchus. 



hi Belly naked 3. Parascaphirhynchus. 



I. Acipenser L. Snout subconical; a small spiracle above the eye; 

 tail subcylindrical and not mailed; pseudobranchiae present: cosmo- 

 politan, in northern waters, both fresh and salt; 5 species in America; 

 the marine species ascend the rivers to breed; the flesh is used for food, 

 the eggs are made into caviar and the air bladder into isinglass; the 

 food of sturgeons consists of small fishes, crayfish, snails, etc. 



Key to the American Species of Acipenser 



ai In the eastern and central States. 



bi In the Atlantic Ocean and its tributaries. 



Ci Space between dorsal and lateral plates with 5 to 10 



rows of small plates A. oxyrhynchiis. 



