30 VERTEBRATE ANIMALS OF THE UNITED STATES 



Key to the Genera of Acipenseridae 



ai Spiracles present i. Acipenser. 



ao Spiracles absent. 



bi Belly covered with subrhombic plates 2. Scaphirhyndius. 



bo Belly naked 3. Parascaphirhynchus. 



I. Acipenser L. Snout subcorneal; 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 .-1. sturio. 



C2 Space between dorsal and lateral plates with very many 



series of minute plates A. brevirostrum. 



b^ In the Great Lakes and upper Mississippi Valley A. rubicundus, 



ao On the Pacific slope. 



bi Lateral plates about 44 A. transmontanus. 



b'l Lateral plates 26 to 30 .4. medirostr is . 



A. sturio L. {A. oxyrhynchus Mitchill.) Common sturgeon. 

 Extreme length 3,600 mm.; extreme weight 550 lbs.; head 3.5; depth 

 5.75; color olive gray, lighter below; dorsal plates 10 to 14; laterals 

 27 to 29; ventrals 8 to 11; rays of dorsal fin 38; anal 27; snout long and 

 sharp, almost as long as the head: Atlantic Ocean and its tributary 

 streams from Maine to South Carolina; often common; a valuable food 

 fish; northern Europe. 



A. breviroslrum heSueur. Short-nosed sturgeon. Length 800 mm.; 

 head 4; depth 5.5; color dusky; snout very short, about a quarter the 

 length of the head; dorsal plates 8 to 11; laterals 22 to 33; ventrals 6 to 

 9; rays of dorsal fin 41; anal 22: Cape Cod to Florida; not common. 



A. rubicundus LeSueur. Lake sturgeon (Fig. 14). Length 1,800 

 mm.; head 3.5; depth 5.75; average weight 50 lbs.; extreme weight 

 100 lbs.; color dark olive, often with large irregular blackish spots; 

 sides paler or reddish; dorsal plates 11 to 15; laterals 38; ventrals 10; 

 rays of dorsal fin 35; anal 26; plates large and rough in the young, 

 becoming smoother and often lost with age: basin of the Great Lakes 



