24 FISHES OF ILLINOIS 



KEY TO ILLINOIS GENERA OF ACIPENSERID^E 



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



snout not shovel-shaped Acipenser. 



a a. 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); spiracles 

 and pseudobranchs present; gill-rakers lance-shaped; air-bladder well devel- 

 oped. Large fishes, numerous in all northern rivers and seas. 



ACIPENSER RUBICUNDUS LE SUEUR 

 LAKE STURGEON; ROCK STURGEON; RED STURGEON 



(PL., p. 36) 



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



G., VIII, 338-339, 341 (rubicundus, maculosus, and liopeltis); J. & G., 87; 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 % greatest width of snout ; lips 2-lobed, the lobes of the lower lip sep- 

 arated by a wide smooth space; barbels of nearly equal length, weakly pec- 

 tinate 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 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 fila- 

 ment as in the shovel-nosed sturgeons; caudal fulcra numerous. Dorsal 

 scutes 12-16, lateral 32-43, ventral 8-10; skin of breast and belly and of 

 sides between scutes more or less densely covered with small rough spinule- 



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



