26. ACIPENSERID^E ACIPENSER. 85 



ally have been unduly multiplied, particularly by Auguste Dumeril, 

 who has found upwards of forty of them in the museum at Paris. 

 The actual number of American sturgeons does not exceed 7, and is 

 more likely still less. 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 disap- 



* 



pear altogether. The number of plates, although one of the best spe- 

 cific characters, is subject to considerable variations. 



(Acipenseridce Giinther, viii, 332-345.) 



* Spiracles present ; snout subconic ; rows of bony shields distinct throughout. 



ACIPEXSER, 47. 

 ** Spiracles obsolete ; snout subspatulate ; rows of bony shields confluent on the tail. 



SCAPHIRRHYXCHOPS, 48. 



9 



47. ACIPENSER* Linnaeus. 

 Sturgeons. 



(Artedi, Linn. Syst. Nat.: type Acipcnser sturio L.) 



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

 by the caudal rays. Gill-rakers small, narrowed or lanceolate. Pseu- 

 dobranchise present. Species numerous. (Latin acipenser, a sturgeon ; 

 from a'zcc, point; nevTa, five?) 







74. A Sturio L. Common Sturgeon. 



Snout rather sharp, nearly as long as the rest of the head, becoming 

 comparatively shorter and blunter with age. Barbels nearly midway 

 between mouth and tip of snout, shortish, not reaching the mouth. 

 Gill-rakers small, slender, pointed, sparse, not longer than the pupil. 



* M. Dunie'iil (Hist. Nat. Poiss. ii, 89) divides this group into six subgenera, as fol- 

 lows : 



a. Spines of dorsal shields situated near their middle. (Mcsocentres.) 

 &. Stellate plates none. 



c. Scutella (between large shields) disposed without order Huso. 



cc. Scutella disposed in quincunx ACIPENSER. 



W). Stellate plates numerous ANTACEUS. 



aa. Spines of dorsal shield at the posterior extremity. (Opisthocentres.) 

 d. Stellate plates none. 



e. Lip emarginate STERLETUS. 



ee. Lip entire LIONISCUS. 



dd. Stellate plates numerous HELOPS. 



The same species at different ages may frequently belong to two or more of these 

 subgenera. 



