ORDER CHOXDROSTEI THE STURGEONS 21 



Order CHONDROSTEI 



(the sturgeons) 



Skeleton chiefly cartilaginous, the vertebral column entirely so; 

 vertebras simple, acentrous, the notochord being persistent; fins without 

 spines ; ventral fins abdominal ; a mesocoracoid arch present ; opercular 

 series represented by an operculum only ; maxillary present ; air-bladder 

 simple, with a well-developed duct. Large fishes of the seas and fresh 

 w^aters of northern regions. A single living family. 



Family ACIPENSERID^ 



(the sturgeons) 



Elongate, subcylindrical fishes, with the head covered with bony 

 plates united by sutures, and with the body armed with 5 longitudinal 

 rows of bony bucklers ; skin of sides between bucklers roughened more or 

 less with small irregular plates or spine-tipped ossicles; skeleton chiefly 

 cartilaginous, the notochord persistent and the vertebrse imperfectly 

 developed; ventral fins abdominal, behind middle of body; dorsal and 

 anal fins posterior; tail heterocercal, its upper lobe covered with rhombic 

 scales; pectorals placed low; gills 4; spiracles developed in some 

 species; an accessory opercular gill; spiracular pseudobranch small or 

 obsolete; no branchiostegals ; an operculum and an interoperculum 

 present; no suboperculum or preoperculum; nostrils double, in front 

 of eye; lateral line present, concealed, traversing the interior of the 

 lateral bucklers; eyes small; optic nerves forming a chiasma; mouth 

 inferior, protractile, with thickened papillose lips; four barbels in a 

 transverse series on lower side of snout in front of mouth ; no teeth except 

 in very young ; stomach without blind sac ; rectum with a spiral valve ; 

 pancreas divided into pyloric appendages ; air-bladder simple, connected 

 with oesophagus by a duct ; arterial bulb with several pairs of valves. 



Sturgeons are widely distributed in the seas, estuaries, and 

 rivers of Europe, Asia, and America, south of the arctic circle, most 

 species being anadromous — that is, living part of the time in salt 

 water and ascending rivers to spavin, as do the salmon and the shad. 

 About 10 species of the genus Acipenser are found along the coasts 

 and in the seas and rivers of Europe and Asia, being most abundant 

 in the Black Sea, the Azov, and the Caspian. Five species are found 

 in North America, two on the Atlantic coast, two on the Pacific 



(3) 



