Jordan and Evermann. Fishes of North America. 103 



anal somewhat behind it, similar; tail heterocercal, the lower caudal lobe 

 developed; the upper lobe of the tail covered with rhomboid scales. Air 

 bladder large, simple, connected with the cesophagus. Pseudobrauchi;u 

 small or obsolete. Stomach without blind sac; rectum with a spiral valve; 

 pancreas divided into pyloric appendages. 



Largo fishes of the seas and fresh waters of northern regions, feeding on 

 small animals and plants sucked in through the tube-like mouth. Most 

 of the species are migratory, like the salmon, which are found in the same 

 waters. Genera 2; species about 20; although more than 5 times that 

 number have been described. The American species especially have been 

 unduly multiplied, particularly by Auguste Dume'ril, who has found up- 

 wards of 40 of them in the museum at Paris. But 6 American species are 

 known to us, and we doubt if any more exist. The changes with age are 

 considerable ; the snout, in particular, becomes much shorter and less acute, 

 and the roughness of the scales is greatly diminished ; the ventral shields 

 sometimes disappear altogether. The number of plates, although one of 

 the best specific characters, is subject to considerable variation. (AciPEN- 

 SERID.E, Gunther, Cat., vm, 332-345.) 



a. Spiracles present; Bnout subconic; rows of bony shields distinct throughout; the tail not 

 depressed nor mailed; gill rakers lanceolate. ACIPENSER, 64. 



a<i. Spiracles obsolete; snout subspatulatc; rows of bony shields confluent behind the dorsal so 

 that the depressed tail is completely mailed; gill rakero small, fan-shaped, ending in 

 3 or 4 points. SCAPHIRHYNCHUS, 65. 



64. ACIPENSER, Linnams. 



(STURGEONS.) 



Acipenser, (ARTEDI), LINNJEUS, Syst. Nat., Ed. x, 1758, 237, (stario). 



Star-to, RAFINESQTJE, Indico Itt. Sicil., 41, 1810, (sturio). 



Slerlelus, RAFINESQUE, Ich. Oh., 79, 1820, (serotinus). 



Dinectus, RAFINESQUE, 7. c., 82, (truncates). 



Huso, BRANDT & RATZEBURG, Medizin. Zool., n, 3, 1833, (huso). 



Sterktus, BRANDT & RATZEBURG, L c., 3, (ruthenus). 



Helops, BRANDT & RATZEBURG, L c., 3, (slellatus). 



Lioniscus, FITZINGER & HECKEL, Ann. Wien. Mus., 370, 1836, (glaber). 



Antaceus, BRANDT, Bull. Ac. Sci. Petersb., v, 138, 1865, (schypa). 



Snout subconical, more or less depressed below the level of the fore- 

 head. A small spiracle over the eye. Caudal peduncle moderately long, 

 deeper than broad, the rows of bony bucklers distinct to the base of tho 

 caudal fin. Tail not produced into a filament, its tip surrounded by the 

 caudal rays. Gill rakers small, narrowed or lanceolate. Pseudobranchiic 

 present. Species numerous in all northern rivers and seas, (acipenser, 

 sturgeon.) 



a. Plates between ventrals and anal small, in 2 rows of 4 to 8; space between dorsal and lateral 



shields with stellate plates of moderate size, in about 5 rows, interspersed with smaller 



ones. Dorsal shields about 12; lateral about 45; ventral about 2. D. 47 ; A. 29. Color 



plain grayish. TRANSMONTANUS, 145. 



aa. Plates between ventrals and anal large, in 1 row, or in 2 rows anteriorly and 1 posteriorly, 



of 1 to 4 plates each. 



b. Space between dorsal and lateral shields with stellate plates of rather lur-e isi/.e, in f. 

 to lOseries; last dorsal shield of moderate size, more thau % length of oue licfore it. 



