FISH OF ONTARIO. 13 



Order CHONDROSTEI. (The Sturgeons.) 



Notochord persistent, the cartilaginous vertebrae imperfectly devel- 

 open. A mesocoracoid. No symplectic bone. Maxillary present. No 

 suboperculum or preoperculum. Interoperculum present. Mesopterygium 

 distinct. Interclavicles present. Basihyals and superior ceratohyal not 

 ossified. Branchihyals osseous. This group is composed of the single 

 family Acipenseridae, represented in our Province by one species. 



Family ACIPENSERID/E. 



Body elongate, subcylindrical, armed with five rows of bony bucklers, 

 each with a median carina which terminates in a spine, which sometimes 

 becomes obsolete with age ; a median dorsal series and a lateral and 

 abdominal series on each side, the abdominal series sometimes deciduous ; 

 between these the skin is rough with small irregular plates. Head covered 

 with bony plates joined by sutures ; snout produced, depressed, conical or 

 subspatulate. Mouth small, inferior, protractile, with thickened lips. No 

 teeth. Four barbels in a transverse series on the lower side of the snout 

 in front of the mouth. Eyes small ; nostrils large, double, in front of eye. 

 Gills, four ; an accessory opercular gill ; gill membranes united to the 

 isthmus ; no branchiostegals. Maxillary distinct from the premaxillary. 

 Head covered with bony plates united by sutures. Fin rays slender, all 

 articulated, vertical fins with fulcra. Pectorals placed low ; ventrals many 

 rayed, behind middle of body ; dorsal placed posteriorly ; 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 oesophagus. Pseudobranchiae small or obso- 

 lete. Stomach without blind sac ; intestine with a spiral valve ; pancreas 

 divided into pyloric appendages. 



Large fishes, feeding on small animals, sucked in through the tube- 

 like mouth. Most of the species are migratory. 



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. 



Genus ACIPENSER. 



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

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

 deeper thari broad, the rows of bony bucklers distinct to the base of the 

 caudal fin. Tail hot produced into a filament, its tip surrounded by the 

 caudal rays. Gill raikers small, narrowed or lanceolate. Pseudobranchiae 

 present. 



