24 FISHES OP ILLINOIS 



Key to Illinois Genera of ACIPENSERID^ 



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 Linnaeus 



(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, 'IS, Trans. Amer. Phil. Soc., 388. 



G. , VIII, 33S-339, 341 (rubicundus, maculosus, and liopeltis) ; J.&G..S7; M.V.,34; 



J. & E., I, 106; N., 51 (maculosus and rubicundus); 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 f 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 2 7 4-6, 

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

 rakers rather broad and covered with fine papillae. Dorsal fin with 

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

 upper caudal lobe considerably longer than -lower, but not produced 

 into a filament as in the shovel-nosed sturgeqns; caudal fulcra numer- 

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



* A single bifid raker was observed on the upper part of the first arch in one 

 specimen. 



