24 fishes of illinois 



Key to Illinois Gexera of ACIPENSERIDjE 



a. Spiracles present; caudal peduncle short, roundish, and incompletely 



armored; snout not shovel-shaped Acipenser. 



aa. Spiracles wanting; caudal peduncle long, flattened, and completely armored; 

 snout broad and shovel-shaped. 



b. Ribs 10 or 11; gill-rakers 2- to 5-pointed; belly and breast wholly covered 



with subrhombic plates Scaphirhynchus. 



bb. Ribs 20 or 21 ; gill-rakers 2- or 3-pointed; belly and breast naked 



Parascaphirhynchus. 



Genus ACIPENSER Linn^us 



(THE STURGEONS) 



Snout not shovel-shaped; caudal peduncle short, roundish, and in- 

 completely armored; lower lip developed only at corners (2-lobed); spir- 

 acles and pseudobranchs present ; gill-rakers lance-shaped ; air-bladder^ 

 well developed. Large fishes, numerous in all northern rivers and seas. 



ACIPENSER RUBICUNDUS Le Sueur 

 (lake sturgeon; rock sturgeon; red sturgeon) 



Le Sueur. '18, Trans. Amor. Phil. Soc, 388. 



G., VIII, 338-339, 341 (rubicundus,maculosus,;md Iiopeltis) ; J .& < '. ,87; M V., 34; 



J. & E., I. 106; X . , 51 (maculosus and rubicundusi; J., 69 (maculosus and 



rubicundus) ; F., 85; L., 7. 



Body elongate, rather slender, nearly cylindrical; depth 7 to 7.8 in 

 length; size large, reaching a length of 6 feet and a weight of 100 lb. 

 Color dark olive above, sides paler or reddish, often with irregular 

 blackish spots; color changing with age, the young drab and the adults 

 green or red. Head 3.1 to 3.8 in length; snout narrow, subconic, 

 strongly convex above, flat below, its length 2 to 2.4 in head (usually 

 less than 2.3); interorbital space 3.2 to 4 in head; eye small, 3.3 to 4.2 

 in interorbital distance; width of mouth about 'j greatest width of snout; 

 lips 2-lobed. the lobes of the lower lip separated by a wide smooth 

 space; barbels of nearly equal length, weakly pectinate on their outer 

 edges; distance between two inner barbels greater than between each 

 inner and outer; gill-membranes united to isthmus; gill-rakers 27+6, 

 lance-shaped*, the surface of the arch between outer and inner rows of 

 rakers rather broad and covered with fine papilla?. Dorsal fin with 

 35 36 rays, its insertion over tips of reflexed ventrals; anal rays 25-28; 

 upper caudal lobe considerably lunger than lower, but not produced 

 into a filamenl as in the shovel-nosed sturgeons; caudal fulcra numer- 

 ous Dorsal scutes 12-16, lateral 32 43, ventral 8 10; skin of lireast 



ingle bifid raker was observed on the upper pari of the first arch in one 



